fix: bound Flat-mode capability manifests

[FreeOnePlus]

Summary

• Limit detected Doris version evidence to each child feature's declared component scope.
• Prevent the Cluster manifest from exceeding the 16 KiB budget and breaking Flat-mode tools/list.
• Add scope-matrix unit coverage and real Doris Flat-mode HTTP/stdio regression coverage.
• Update CHANGELOG.md under Unreleased.

Validation

• uv lock --check
• uv run ruff check .
• uv run mypy doris_mcp_server
• uv run bandit -q -c pyproject.toml -r doris_mcp_server
• uv build
• pytest -W error -q: 1722 passed, 81 skipped; 67.37% coverage
• Real Doris 4.0.5-rc01 Flat-mode regression over HTTP and stdio: 2 passed; 47 tools listed; read-only version query succeeded
• Real manifest audit: all eight domains within budget; Cluster manifest 16,325 / 16,384 bytes