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

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

feat: enhance embedding model configuration and retrieval logic

feat: enhance AI involvement handling and transparency metrics

fix: allow reference-only RAG guidance in notes-only mode

refactor: enhance non-invention guard and tier-aware output handling

- 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.

- Introduced `ingest_timeout_seconds` setting in config.py to define maximum time for document ingestion.

Merge origin/experiment-lab (LangChain RAG) into experiment-lab + product features

feat: enhance document upload and processing capabilities with new personalisation features

feat(experiment-lab): rewrite RAG pipeline using LangChain framework

fix: comprehensive codebase review fixes (critical + major + minor issues)

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