Consistent and strict type hints improve maintainability, IDE autocompletion, and static analysis accuracy.

This issue proposes to:

• Add explicit type hints to __aexit__ methods (currently untyped in core/rate_limit.py).
• • Add return type hints to lifespan and other @asynccontextmanager methods (e.g., in api/app.py and messaging/trees/data.py).
• • • Tighten type hints for configuration validators in config/settings.py to avoid Any where possible.
• • • • Improve Ollama base URL validation error message for better clarity.
        While the current ty check may pass without these, adding them ensures the codebase adheres to the strict engineering standards mentioned in AGENTS.md.