Update OpenAPI documentation and docstrings for strict filter field and prefixing changes (PR #1291) #1306

This change introduces strict filter field validation and a new metadata prefixing requirement for filters (see PR #1291).

We generate and publish openapi.json automatically from docstrings. Please ensure the OpenAPI docstrings describing filter objects, filter_dict usage, and accepted query syntax are up-to-date and clarify:

• All user metadata fields must be prefixed with m. or metadata.
• Filters with unknown or misspelled fields now result in 400 errors.

Deliverables:

• Review all API endpoint descriptions that declare filter_dict, query string filters, or filter syntax (especially endpoints for search, querying, semantic memory, etc.).
• Bring all docstrings and OpenAPI output into alignment with new prefixing and error behavior.
• Generate a new openapi.json artifact and submit for review.

Reference: PR #1291