refactor: separate tool catalog from manager

[FreeOnePlus]

Summary

• move immutable MCP tool metadata and schemas into a standalone catalog module
• keep lifecycle, authorization, audit, handler execution, and routing in DorisToolsManager
• add architectural boundary tests and update contributor guidance

Validation

• uv run ruff check .
• uv run mypy doris_mcp_server
• uv run bandit -q -c pyproject.toml -r doris_mcp_server
• uv run pytest -q -W error — 1027 passed, 68 skipped
• real Doris Streamable HTTP + subprocess Stdio — 11 passed, residual tables/users 0
• official MCP server-stateless Conformance — 25/25 passed
• clean sdist/wheel build and Python 3.12 wheel import smoke

Ledger item: CORE-009