docs(hf): add 28_Solana_Semantic_Anchor/README.md matching whitepaper standard

28_Solana_Semantic_Anchor/README.md

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+# 28. Solana Semantic Anchor & Payments Gateway
+
+![Language-U Logo](./assets/language_u_logo.jpg)
+
+This directory implements the on-chain attestation and payments incentive layers for the **Language-U Semantic Communication Protocol** on the **Solana** blockchain.
+
+---
+
+## 🏗️ Components
+
+1.  **Anchor Smart Contract (`solana-cuneiform-anchor`):**
+    *   Located in `programs/solana-cuneiform-anchor/src/lib.rs`
+    *   Defines the on-chain PDA account `CoordinateRecord` to store the 6D semantic coordinates (`[DOMAIN, SUBDOMAIN, MODALITY, POLARITY, STRENGTH, DEPTH]`) and corresponding cryptographic `merkle_root` signatures of intents.
+    *   Instructions:
+        *   `register_coordinates`: Initializes a coordinate record on-chain.
+        *   `update_coordinates`: Mutates coordinates, restricted to the original authority.
+2.  **TypeScript SDK Client:**
+    *   Located in `app/src/cuneiform_client.ts`
+    *   An ESM-compliant helper to serialize instructions and deserialize accounts dynamically (calculating discriminators via SHA-256) without requiring a pre-compiled JSON IDL.
+3.  **Solana Pay Mesh Gateway:**
+    *   Located in `app/src/solana_pay_mock.ts`
+    *   Compiles standards-compliant Solana Pay request URLs to handle micro-payments (USDC/USDG) to reward mesh routing nodes.
+
+---
+
+## 🧪 Running the Tests
+
+1. Install dependencies:
+   ```bash
+   npm install
+   ```
+2. Run the integration test suite (validates PDA derivations, mock account deserializations, and Solana Pay URI compliance):
+   ```bash
+   node tests/solana-cuneiform-anchor-standalone.js
+   ```
+
+---
+
+## 🦀 Building the Rust Program
+
+Ensure Cargo is installed, then check compilation via:
+```bash
+cargo check
+```