Filter media and groups by favorite state

[MinasukiHikimuna]

Summary

Add a consistent Favorite criterion to video, image, audio, text, gallery, and group list filters. The criterion filters against the signed-in user's affinity state, composes with existing criteria, renders the standard applied-filter chip, and is preserved by saved filters.

Favorite: No includes both explicit non-favorites and entities without an affinity row. The same behavior is used by normal list and aggregate queries, with matching support in filter-backed dynamic audio and text groups.

Linked issue

Closes #430

Type of change

• Bug fix
• New feature
• Refactor / tech debt
• Docs
• Other: N/A

AI usage

• No AI was used for this PR.
• AI was used for this PR.
  • Model(s): GPT-5.6 Sol
  • Where / how: Issue investigation, live UI reproduction, implementation, regression tests, verification, and independent code review.
• A human (me) has reviewed, understands, and takes full responsibility for every change here including that the design and architecture are sound. (required)

Testing done & evidence

• Confirmed before the change that supported media and group lists did not expose their own Favorite criterion, while an existing entity filter demonstrated the expected boolean editor and applied-chip behavior.
• Added backend behavior probes for all six entity types. The regression-first run failed the six new positive probes as expected; after implementation, the focused harness completed successfully with 60/60 tests passing, including Favorite: No behavior for entities without affinity rows:
  • dotnet test src/Cove.Tests/Cove.Tests.csproj --configuration Release --no-build --no-restore --filter "FullyQualifiedName~Cove.Tests.EntityListSortBehaviorHarnessTests.RepresentativeFiltersMatchSeededFixtureSet" --logger "console;verbosity=normal"
• Built the affected test project in Release successfully with 0 errors:
  • dotnet build src/Cove.Tests/Cove.Tests.csproj --configuration Release --no-restore
• Passed the required solution-wide Release build with 0 errors and four existing xUnit analyzer warnings:
  • dotnet build src/Cove.slnx -c Release --no-restore
• Passed frontend filter-definition coverage with 19/19 tests:
  • npm test -- --run src/test/filterCriteriaDefinitions.test.ts
• Passed filter-dialog and saved-filter coverage with 79/79 tests:
  • npm test -- --run src/test/FilterDialog.test.tsx src/test/SavedFilterMenu.test.tsx
• Passed the focused saved-filter persistence test file with 9/9 tests after updating it to serialize favoriteCriterion:
  • npm test -- --run src/test/SavedFilterMenu.test.tsx
• Completed the production frontend build successfully:
  • npm run build
• Restarted the development API and verified through the live UI that Favorite is available alongside the existing criteria, applying Favorite: Yes sends a successful filtered-list request, reduces the list to the matching result, and renders an applied Favorite: Yes chip.
• An independent xhigh code review found no blocking correctness, regression, test, or complexity issues.

Checklist

• I have read and followed the Contribution Guide.
• Builds and existing tests pass.
• I added or updated tests where it makes sense.
• I updated docs where needed.
• This PR is focused and does not bundle unrelated changes.