Enhance environment configuration and API documentation for Milestone 11

Implement Milestone 8 by adding new endpoints for URL ingestion and collection management. Introduce `httpx` as a dependency for handling URL downloads, and enhance the API with endpoints for listing and deleting collections. Update request and response models to support new functionalities, and refactor existing routes for improved clarity and organization.

Implement Milestone 7 by introducing background ingestion jobs. Update environment configuration to include job database path, enhance job tracking with new endpoints, and refactor ingestion logic to support asynchronous processing. Modify response models to include job details and ensure proper initialization of the jobs database on startup.

Implement Milestone 6 by adding audit persistence functionality. Introduce `aiosqlite` as a dependency, update the audit routes to support event logging and retrieval, and enhance the query endpoint to persist audit records. Modify response models to include audit details and ensure proper initialization of the audit database on startup.

Implement Milestone 5 by adding retrieval and grounded LLM answer functionality. Update query endpoint to return grounded answers with source citations, enhance response models to include answer and sources, and refactor retriever logic to support new chunk structure and grounding mechanism. Update milestones documentation to reflect new dependencies and expected outputs.

Implement Milestone 3 by adding configuration and request/response contracts. Introduce new models for requests and responses, enhance route handlers with schema validation, and update dependencies to include pydantic-settings. Update audit, ingest, jobs, and query routes to utilize new models and improve response structures.