Migrate inventory read to FastAPI

[cbusillo]

Summary

• add a native FastAPI GET /v1/inventory/{context}/{instance} route with typed response and OpenAPI contract coverage
• pre-authorize inventory.read against the path context before store access, then verify the stored inventory context before returning the record
• remove the legacy WSGI inventory read matcher/handler and document the retirement

Refs #1322

Validation

• uv run python -m unittest tests.test_http_app.FastApiEnvironmentInventoryReadTests tests.test_service.LaunchplaneServiceTests.test_single_record_read_routes_are_retired_from_legacy_wsgi_app
• uv run python -m unittest tests.test_http_app tests.test_service
• uv run python -m unittest
• uv run --extra dev ruff check --diff .
• uv run --extra dev ruff check .
• uv run --extra dev ruff check control_plane/http_app.py control_plane/service.py tests/test_http_app.py tests/test_service.py
• uv run --extra dev ruff format --check control_plane/http_app.py control_plane/service.py tests/test_http_app.py tests/test_service.py
• uv run --extra dev mypy control_plane tests
• JetBrains changed-files closeout: clean
• two read-only review agents: green to merge

Notes

• uv run --extra dev ruff format --check . still reports 56 unrelated pre-existing files that would reformat; changed Python files are formatted.