Add backend configuration system (#1)

- Create Settings class with Pydantic validation
- Define file processing limits (50MB max, type restrictions)
- Add CORS configuration for frontend integration
- Create .env.example template for environment setup
- Update requirements.txt with core dependencies

Why: Centralized config prevents hardcoded values and enables
environment-based configuration for dev/prod.

backend/.env.example

@@ -0,0 +1,14 @@
+# Server Configuration
+DEBUG=False
+HOST=0.0.0.0
+PORT=8000
+
+# File Processing
+MAX_FILE_SIZE_MB=50
+
+# CORS (Update with your frontend URL)
+CORS_ORIGINS=["http://localhost:3000"]
+
+# Future: Add API keys for AI models here
+# OPENAI_API_KEY=your_key_here
+# HUGGINGFACE_TOKEN=your_token_here

backend/core/config.py

@@ -0,0 +1,40 @@
+"""
+Application configuration management.
+Uses environment variables for security-sensitive settings.
+"""
+from pydantic_settings import BaseSettings
+from typing import Optional
+
+
+class Settings(BaseSettings):
+    """
+    Application settings loaded from environment variables.
+    
+    Why Pydantic? Type validation, auto-documentation, easy testing.
+    """
+    # API Settings
+    API_TITLE: str = "VeriFile-X API"
+    API_VERSION: str = "0.1.0"
+    API_DESCRIPTION: str = "Privacy-preserving digital forensics platform"
+    
+    # Server Settings
+    HOST: str = "0.0.0.0"
+    PORT: int = 8000
+    DEBUG: bool = False
+    
+    # File Processing Limits (privacy + performance)
+    MAX_FILE_SIZE_MB: int = 50
+    ALLOWED_IMAGE_TYPES: list = ["image/jpeg", "image/png", "image/webp"]
+    ALLOWED_VIDEO_TYPES: list = ["video/mp4", "video/mpeg"]
+    ALLOWED_DOC_TYPES: list = ["application/pdf"]
+    
+    # Security
+    CORS_ORIGINS: list = ["http://localhost:3000"]  # Frontend URLs
+    
+    class Config:
+        env_file = ".env"
+        case_sensitive = True
+
+
+# Singleton pattern - one instance across app
+settings = Settings()

backend/requirements.txt

@@ -0,0 +1,17 @@
+# Web Framework
+fastapi==0.109.0
+uvicorn[standard]==0.27.0
+
+# Configuration Management
+pydantic==2.5.3
+pydantic-settings==2.1.0
+python-dotenv==1.0.0
+
+# File Processing
+python-magic==0.4.27
+python-multipart==0.0.6
+
+# Future AI/ML dependencies (add as needed)
+# opencv-python==4.9.0.80
+# tensorflow==2.15.0
+# numpy==1.24.3