feat: Added request logging middleware to the backend

[yughpatel]

📋 PR Checklist

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🔗 Related Issue

Closes #36

📝 What does this PR do?

This PR implements custom structured JSON logging using loguru for the backend, replacing generic console logging with meaningful, context-rich logging tailored to RAG workflows:

1. Structured Logging Middleware: Implements StructuredLoggingMiddleware to capture core HTTP metrics (method, path, status code, response time in ms), unique request IDs (X-Request-ID), and authenticated user IDs.
2. Context-Aware Fields: Automatically binds application-specific context variables across the request lifecycle:
   • Uploads: Logs the filename and file_size on document uploads (/upload and /urlupload).
   • Chat Queries: Logs the query text and chunks_retrieved count from the vector database on RAG chat queries and streams (/chat/ask and /chat/ask/stream).
3. Standard Log Redirection: Intercepts standard python logging outputs (including FastAPI, Uvicorn, and SQLAlchemy) and redirects them through loguru to maintain a single JSON log schema.
4. Rotation and Levels: Configures Loguru with file-based rotation (10 MB), retention (10 days), and compression (zip) written to ./data/logs/app.log, loading environment-based log levels (LOG_LEVEL=DEBUG in development, INFO in production).
5. Documentation: Overwrote CONTRIBUTING.md with guidelines on branch rules, development setup, and hook rules.

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🗂️ Type of Change

• 🐛 Bug fix
• ✨ New feature
• 🔧 Refactor / code cleanup
• 📝 Documentation update
• 🎨 UI / styling change
• ⚙️ CI / tooling / config change
• 🧪 Tests

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🧪 How was this tested?

• Ran the backend locally (uvicorn app.main:app --reload)
• Tested the affected API endpoints manually
  Details:
• Ran a local uvicorn server in a clean Python 3.14 environment.
• Executed end-to-end integration tests (user registration, login, document upload, RAG ask, and RAG streaming) verifying that requests correctly write clean, single-line JSON log outputs containing all request-local context parameters to console stdout and backend/data/logs/app.log.

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📸 Screenshots (if UI change)

N/A

⚠️ Anything to flag for reviewers?

• Added loguru as a new backend dependency in requirements.txt.
• Local contextvars were combined with FastAPI request.state to ensure robust parameter propagation back to the middleware logs across different asyncio task environments.

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✅ Self-Review Checklist

• My branch is based on dev, not main
• I have not added any secrets / API keys
• I have not modified main branch or any HuggingFace deployment config
• My code follows the existing style (no unnecessary formatting changes)
• I have updated relevant docs / comments if needed

[param20h]

resolve conflicts
@yughpatel

[yughpatel]

resolve conflicts
@yughpatel

Will work on it