feat(catalog): support shared provider metadata

[typelicious]

Summary

• add a shared provider metadata overlay loader for Gate via file or repo-backed JSON snapshots
• add sync hooks so restart/update flows can materialize provider metadata snapshots automatically
• add tests and planning docs for the fusionAIze-only shared metadata repo shape

Validation

• rtk ruff check faigate/provider_catalog.py tests/test_provider_catalog.py
• python3 -m pytest -q tests/test_provider_catalog.py