feat: implement audit trail system

[codewithzubair07]

🚀 Audit Trail Implementation

📌 Description

This PR introduces an audit trail system to track API actions, user activities, and system events with tamper-proof logging.

---

✅ Features

• Automatic logging using NestJS interceptor
• Tracks API actions (CRUD + auth events)
• Tamper-proof logs using SHA-256 hashing
• Audit log entity with structured metadata
• Endpoint to retrieve logs (GET /audit)

---

⚙️ Implementation

• Created AuditModule, AuditService, and AuditLog entity
• Added global interceptor for automatic logging
• Integrated module into AppModule and main.ts
• Logs are immutable (no update/delete operations)

---

⚠️ Notes

• Existing TypeScript errors in the repository are unrelated to this PR
• No unrelated files were modified

---

🧪 Testing

• Verified logs are created automatically for API requests
• Logs can be retrieved via API endpoint
  closes [DB] Audit Trail Implementation #152