test(data): add zustand store unit tests and fix annotation-store selector hooks

[WilliamBerryiii]

Comprehensive unit tests for all Zustand stores in the Dataset Analysis Tool frontend, targeting 80%+ coverage for Issue #217. Alongside the new tests, a performance bug was discovered and fixed in annotation-store.ts where selector hooks created new object references on every store update, causing unnecessary component re-renders.

Description

Closes #217

Bug Fix

The five selector hooks in annotation-store.ts (useAnnotationDirtyState, useTaskCompletenessState, useTrajectoryQualityState, useDataQualityState, useAnomalyState) returned new object references on each store update. Wrapped all five with useShallow from zustand/react/shallow and extracted an EMPTY_ANOMALIES constant to stabilize return values and prevent unnecessary re-renders.

Test Coverage

Added and expanded tests across seven test files covering the full Zustand store layer:

• Annotation store — 5 new selector hook tests validating dirty state, task completeness, trajectory quality, data quality, and anomaly reference stability
• Edit store action factories — 14 frame action tests, subtask CRUD and reorder tests, and transform action tests using reusable state factory helpers
• Edit store helpers — tests for buildOriginalEditState, buildEditOperations, hasEditContent, computeDirty, and persistEditStateDraft
• Edit store selectors — 6 selector hooks tested via renderHook covering transforms, frame removal/insertion, subtask operations, dirty state, and trajectory adjustments
• Edit store frame utilities — 11 edge case tests for frame index mapping and frame count calculations with boundary conditions
• Episode store — setLoading action test plus 3 selector hook tests for episode index, navigation, and playback
• Joint config store — idempotency guard test for initDefaults

All tests follow existing codebase conventions: renderHook() for hook isolation, vi.mock() for dependencies, beforeEach cleanup, and act() wrapping for state mutations.

Type of Change

• 🐛 Bug fix (non-breaking change fixing an issue)
• ✨ New feature (non-breaking change adding functionality)
• 💥 Breaking change (fix or feature causing existing functionality to change)
• 📚 Documentation update
• 🏗️ Infrastructure change (Terraform/IaC)
• ♻️ Refactoring (no functional changes)

Component(s) Affected

• data-management/viewer/frontend/src/stores/ — Zustand stores and tests

Testing Performed

• 658 tests passing via Vitest 4.1.0 + Happy DOM 20.8.9
• All new and existing store tests pass
• No new linting warnings introduced

Documentation Impact

• No documentation changes needed
• Documentation updated in this PR
• Documentation issue filed

Bug Fix Checklist

• Linked to issue being fixed
• Regression test included
  • Selector hook tests verify useShallow wrapping produces stable references

Checklist

• My code follows the project conventions
• Commit messages follow conventional commit format
• I have performed a self-review
• Documentation impact assessed above
• No new linting warnings introduced

🤖 - Generated by Copilot

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Snapshot Warnings

⚠️: No snapshots were found for the head SHA e93457c.

Ensure that dependencies are being submitted on PR branches and consider enabling retry-on-snapshot-warnings. See the documentation for more information and troubleshooting advice.

Scanned Files

None

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.80%. Comparing base (5fb6d58) to head (e93457c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #452      +/-   ##
==========================================
+ Coverage   64.41%   64.80%   +0.38%     
==========================================
  Files         251      251              
  Lines       15435    15441       +6     
  Branches     2108     2060      -48     
==========================================
+ Hits         9942    10006      +64     
+ Misses       5205     5146      -59     
- Partials      288      289       +1     

Flag	Coverage Δ
pester	82.24% <ø> (ø)
pytest	92.40% <ø> (ø)
pytest-dataviewer	63.87% <ø> (ø)
pytest-fuzz	1.59% <ø> (ø)
vitest	51.77% <100.00%> (+0.97%)	⬆️

Files with missing lines	Coverage Δ
...ent/viewer/frontend/src/stores/annotation-store.ts	85.71% <100.00%> (+9.65%)	⬆️

... and 6 files with indirect coverage changes

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