feat: async pipeline, job queue, generation hardening, and docs

chore: update .gitignore and README for improved clarity and functionality

- Added support for RICS survey levels (1, 2, 3) in document uploads and reports, allowing for better tier management and retrieval filtering.

- Replaced timezone.utc with UTC from datetime for consistent datetime handling.

- Updated `.env.example` to include new settings for bulk upload limits and batch processing.

feat: scaffold complete RAG system for RICS-style report generation