feat: refactor server tools and add health checks

[gettingstuffdone]

Description:
This PR refactors the Python server's tool organization and adds stability enhancements:

• Tool Reorganization: Moved core tool logic from server/main.py into a structured server/tools/ package.
• Formatting Logic: Extracted Markdown table and result formatting into server/tools/formatting.py for better reuse.
• Health Check: Added a /health endpoint to the Python server to allow the Go gateway to monitor worker status.
• Iceberg Bug Fix: Corrected S3 path parsing in catalog/iceberg.py to handle trailing slashes in table prefixes.
• Simplified Workflow: Merged estimate_query into datalake_query via a new explain_only flag, streamlining the MCP toolset.
• Test Coverage: Added unit tests for the Iceberg metadata reader (server/tests/test_iceberg_reader.py).
• Cleanup: Updated .gitignore to exclude local config/config.yaml.

[endemics]

Why removing the warning here?

[gettingstuffdone]

this should be restored now