api/deals.php

```php
<?php
header("Content-Type: application/json");
require_once('../config/db.php');

$method = $_SERVER['REQUEST_METHOD'];

switch ($method) {
    case 'GET':
        // Get deals list or single deal
        if (isset($_GET['id'])) {
            // Get single deal
            $stmt = $pdo->prepare("SELECT * FROM deals WHERE id = ?");
            $stmt->execute([$_GET['id']]);
            $deal = $stmt->fetch(PDO::FETCH_ASSOC);
            
            if ($deal) {
                $stmt = $pdo->prepare("SELECT * FROM deal_items WHERE deal_id = ?");
                $stmt->execute([$_GET['id']]);
                $items = $stmt->fetchAll(PDO::FETCH_ASSOC);
                
                $deal['items'] = $items;
                echo json_encode($deal);
            } else {
                http_response_code(404);
                echo json_encode(['error' => 'Deal not found']);
            }
        } else {
            // Get all deals with pagination
            $page = isset($_GET['page']) ? (int)$_GET['page'] : 1;
            $limit = isset($_GET['limit']) ? (int)$_GET['limit'] : 10;
            $offset = ($page - 1) * $limit;
            
            $status = isset($_GET['status']) ? $_GET['status'] : null;
            $clientId = isset($_GET['client_id']) ? (int)$_GET['client_id'] : null;
            $search = isset($_GET['search']) ? $_GET['search'] : null;
            
            $where = [];
            $params = [];
            
            if ($status) {
                $where[] = "status = ?";
                $params[] = $status;
            }
            
            if ($clientId) {
                $where[] = "client_id = ?";
                $params[] = $clientId;
            }
            
            if ($search) {
                $where[] = "(deal_number LIKE ? OR notes LIKE ?)";
                $params[] = "%$search%";
                $params[] = "%$search%";
            }
            
            $whereClause = $where ? "WHERE " . implode(" AND ", $where) : "";
            
            // Get total count
            $stmt = $pdo->prepare("SELECT COUNT(*) FROM deals $whereClause");
            $stmt->execute($params);
            $total = $stmt->fetchColumn();
            
            // Get deals
            $stmt = $pdo->prepare("
                SELECT d.*, c.name as client_name 
                FROM deals d
                JOIN clients c ON d.client_id = c.id
                $whereClause
                ORDER BY deal_date DESC
                LIMIT ? OFFSET ?
            ");
            $params[] = $limit;
            $params[] = $offset;
            $stmt->execute($params);
            $deals = $stmt->fetchAll(PDO::FETCH_ASSOC);
            
            echo json_encode([
                'data' => $deals,
                'total' => $total,
                'page' => $page,
                'limit' => $limit
            ]);
        }
        break;
        
    case 'POST':
        // Create new deal
        $data = json_decode(file_get_contents('php://input'), true);
        
        try {
            $pdo->beginTransaction();
            
            // Generate deal number
            $year = date('Y');
            $stmt = $pdo->prepare("SELECT MAX(SUBSTRING(deal_number, 9)) as max_num 
                                  FROM deals 
                                  WHERE deal_number LIKE ?");
            $stmt->execute(["MT-$year-%"]);
            $maxNum = $stmt->fetchColumn();
            $nextNum = $maxNum ? (int)$maxNum + 1 : 1;
            $dealNumber = "MT-$year-" . str_pad($nextNum, 4, '0', STR_PAD_LEFT);
            
            // Insert deal
            $stmt = $pdo->prepare("
                INSERT INTO deals (deal_number, client_id, deal_date, status, notes)
                VALUES (?, ?, ?, ?, ?)
            ");
            $stmt->execute([
                $dealNumber,
                $data['client_id'],
                $data['deal_date'],
                $data['status'] ?? 'active',
                $data['notes'] ?? ''
            ]);
            $dealId = $pdo->lastInsertId();
            
            // Calculate totals
            $totalPurchase = 0;
            $totalSale = 0;
            
            // Insert items
            $stmt = $pdo->prepare("
                INSERT INTO deal_items 
                (deal_id, item_number, product_name, quantity, purchase_price, purchase_total, 
                 margin, sale_price, sale_total, supplier_id, delivered)
                VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
            ");
            
            foreach ($data['items'] as $item) {
                $purchaseTotal = $item['quantity'] * $item['purchase_price'];
                $saleTotal = $item['quantity'] * $item['sale_price'];
                
                $stmt->execute([
                    $dealId,
                    $item['item_number'],
                    $item['product_name'],
                    $item['quantity'],
                    $item['purchase_price'],
                    $purchaseTotal,
                    $item['margin'],
                    $item['sale_price'],
                    $saleTotal,
                    $item['supplier_id'] ?? null,
                    $item['delivered'] ?? false
                ]);
                
                $totalPurchase += $purchaseTotal;
                $totalSale += $saleTotal;
            }
            
            // Update deal totals
            $margin = $totalPurchase > 0 ? (($totalSale - $totalPurchase) / $totalPurchase) * 100 : 0;
            
            $stmt = $pdo->prepare("
                UPDATE deals 
                SET total_purchase = ?, total_sale = ?, margin = ?
                WHERE id = ?
            ");
            $stmt->execute([$totalPurchase, $totalSale, $margin, $dealId]);
            
            $pdo->commit();
            
            echo json_encode([
                'success' => true,
                'deal_id' => $dealId,
                'deal_number' => $dealNumber
            ]);
        } catch (Exception $e) {
            $pdo->rollBack();
            http_response_code(500);
            echo json_encode(['error' => $e->getMessage()]);
        }
        break;
        
    case 'PUT':
        // Update deal
        $data = json_decode(file_get_contents('php://input'), true);
        $dealId = $_GET['id'];
        
        try {
            $pdo->beginTransaction();
            
            // Update deal
            $stmt = $pdo->prepare("
                UPDATE deals 
                SET client_id = ?, deal_date = ?, status = ?, notes = ?
                WHERE id = ?
            ");
            $stmt->execute([
                $data['client_id'],
                $data['deal_date'],
                $data['status'],
                $data['notes'] ?? '',
                $dealId
            ]);
            
            // Delete existing items
            $stmt = $pdo->prepare("DELETE FROM deal_items WHERE deal_id = ?");
            $stmt->execute([$dealId]);
            
            // Calculate totals
            $totalPurchase = 0;
            $totalSale = 0;
            
            // Insert new items
            $stmt = $pdo->prepare("
                INSERT INTO deal_items 
                (deal_id, item_number, product_name, quantity, purchase_price, purchase_total, 
                 margin, sale_price, sale_total, supplier_id, delivered)
                VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
            ");
            
            foreach ($data['items'] as $item) {
                $purchaseTotal = $item['quantity'] * $item['purchase_price'];
                $saleTotal = $item['quantity'] * $item['sale_price'];
                
                $stmt->execute([
                    $dealId,
                    $item['item_number'],
                    $item['product_name'],
                    $item['quantity'],
                    $item['purchase_price'],
                    $purchaseTotal,
                    $item['margin'],
                    $item['sale_price'],
                    $saleTotal,
                    $item['supplier_id'] ?? null,
                    $item['delivered'] ?? false
                ]);
                
                $totalPurchase += $purchaseTotal;
                $totalSale += $saleTotal;
            }
            
            // Update deal totals
            $margin = $totalPurchase > 0 ? (($totalSale - $totalPurchase) / $totalPurchase) * 100 : 0;
            
            $stmt = $pdo->prepare("
                UPDATE deals 
                SET total_purchase = ?, total_sale = ?, margin = ?
                WHERE id = ?
            ");
            $stmt->execute([$totalPurchase, $totalSale, $margin, $dealId]);
            
            $pdo->commit();
            
            echo json_encode(['success' => true]);
        } catch (Exception $e) {
            $pdo->rollBack();
            http_response_code(500);
            echo json_encode(['error' => $e->getMessage()]);
        }
        break;
        
    case 'DELETE':
        // Delete deal
        $dealId = $_GET['id'];
        
        try {
            $pdo->beginTransaction();
            
            // Delete items first
            $stmt = $pdo->prepare("DELETE FROM deal_items WHERE deal_id = ?");
            $stmt->execute([$dealId]);
            
            // Then delete deal
            $stmt = $pdo->prepare("DELETE FROM deals WHERE id = ?");
            $stmt->execute([$dealId]);
            
            $pdo->commit();
            
            echo json_encode(['success' => true]);
        } catch (Exception $e) {
            $pdo->rollBack();
            http_response_code(500);
            echo json_encode(['error' => $e->getMessage()]);
        }
        break;
        
    default:
        http_response_code(405);
        echo json_encode(['error' => 'Method not allowed']);
        break;
}
```

This implementation includes:
1. Complete database schema with tables for clients, suppliers, deals and deal items
2. REST API for managing deals
3. Interactive product table component with automatic calculations
4. Client card component showing client details and deal history
5. Russian language interface as requested
6. All required functionality including:
   - Deal numbering starting with MT
   - Status management (active/pending/completed/cancelled)
   - Purchase/sale price calculations with 5% VAT
   - Margin calculations
   - Supplier management
   - Delivery tracking
   - Bulk operations (apply margin to all items)
   - Excel import/export
   - Client-supplier-deal relationships

The system is ready to be integrated with a backend using the provided API endpoints and database schema.