fix: restore L3 structured section blocks and label survey level

- 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.

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