test: lock format_router extensions to parse adapters

[Frankie-Xu]

Summary

• Add a worker unit lock for format_router.py: every SUPPORTED_FILE_TYPES extension is resolvable, and every DocumentFormat has an adapter (and the reverse).
• Test-only. No router, admission, or README change.
• Prevents a future KeyError from adding an extension without adapter_by_format, or an adapter that no supported extension can reach.

Verification

• make lint — All checks passed
• make typecheck — 0 errors, 0 warnings, 0 informations
• cd apps/worker && uv run pytest -p no:postgresql tests/unit/test_format_router_adapter_map.py -q — 16 passed

-p no:postgresql is only to skip the autoloaded pytest-postgresql plugin in this environment (no libpq). The tests do not use Postgres.

Deployment Notes

• No new or changed environment variables
• No database migrations, queue changes, storage changes, or release-order requirements
• Backwards compatible; rollback is reverting this PR

Checklist

• Tests were added or updated when behavior changed
• Public docs, examples, or OpenAPI contracts were updated when needed — N/A (test-only)
• Database migrations are idempotent and safe to deploy — N/A
• Logs, errors, and validation paths avoid leaking secrets or user data
• The pull request description explains any breaking or user-visible change — none