Review fixes for the Affiliation Catalogs plugin

[moliholy]

This PR applies the fixes from a review of indico#6 (Affiliation Catalogs). It targets the PR branch (affiliation-schemas) so the diff is only the fixes.

What this fixes

Correctness

• Editing a registration after the catalog config changed (list disabled or removed, default catalog switched) no longer fails. The representation field skips re-validation when its stored value is unchanged, so unrelated edits to a registration keep working.
• Duplicate affiliation list names within a catalog are now rejected (server and client), matching the contact-list behavior.

Performance

• Inherited default-catalog resolution no longer runs get_all_catalogs once per ancestor category; it resolves the whole chain in a single query. This path runs on every registration form render.

Client

• The "See affiliations" modal no longer crashes when the resolve request fails or returns nothing.
• Unsaved catalog list rows now use stable keys, so reordering or deleting rows before saving no longer attaches input state to the wrong row.
• Fixed the "invalid contact emails" warning, which was shown whenever any affiliation existed.
• Removed a dead dashboard/types.ts module whose only import pointed at a nonexistent path.

Robustness and polish

• models/__init__.py now imports every model, so importing the package registers all SQLAlchemy mappers regardless of import order.
• User-facing validation messages in the representation field and catalog code are wrapped in _() for translation.
• Added a conftest.py that mocks the plugin webpack manifest so management pages render in tests. This is the fix for the failing test-plugin (affiliation_extras) CI job (assets are not built in CI).

Verification

• pytest: 73 passed (includes 2 new regression tests).
• ruff check and ruff format --check: clean, run against the core branch from Add "Affiliation" field type for registration forms indico/indico#7352.

Note: the base here is affiliation-schemas, not master, so the repo's CI (which only runs on PRs targeting master/*.x) will not trigger automatically. Everything above was verified locally.

Deliberately not changed (need a decision)

• 403-vs-404 on cross-scope catalog ids: returning 403 is locked in by an existing test; treating out-of-scope as 404 is a design call.
• Regform managers can resolve global user emails by affiliation, while the sibling invite endpoints are admin-only. Confirm the intended trust level.
• Cloning an inherited catalog copies parent-defined group/tag/affiliation membership into the child. Confirm intent.
• The contact-list functional unique-index name mismatch is pre-existing (from Add Extended Affiliations plugin indico/indico-plugins-contrib#2's migration chain), not introduced here.