feat: AI interference levels (minimum|medium|maximum) UI, API, prompts, generation

- 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.

fix: apply all bug fixes and improvements (embeddings, cache, postprocess, frontend, tests)

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