test(dataviewer): add tests for remaining feature components

[WilliamBerryiii]

Problem Statement

After completing the focused component test issues (#214–#221), some components will remain untested — shared UI primitives, layout wrappers, context providers, error boundaries, routing components, and feature-specific components not covered by the earlier issues. This catch-all issue covers the remaining gap to reach 80% overall frontend coverage.

Parent tracking issue: #210
Depends on: All prior test issues (#211–#221)

Scope

Remaining untested areas (examples — actual scope determined by coverage gaps):

• Shared UI components (buttons, modals, tooltips, dropdowns)
• Layout components (sidebar, header, footer, split panes)
• Context providers and their consumer patterns
• Error boundary components
• Route components and navigation guards
• Any feature components not covered by issues test(dataviewer): add tests for episode viewer components #218–test(dataviewer): add tests for frame editor components #221

Acceptance Criteria

• All remaining untested components have corresponding .test.tsx files
• Tests follow the same patterns established in earlier issues
• Error boundaries tested with error-throwing children
• Context providers tested with consumer components
• Overall src/ coverage reaches 80% for lines, functions, branches, and statements
• npm run test:coverage passes with thresholds enforced
• All new tests pass with npm run test

How to Identify Remaining Gaps

Run npm run test:coverage and check the coverage report for files below 80%. Prioritize:

1. Files with 0% coverage
2. Files with complex logic below threshold
3. Files with high usage (imported by many other files)

RPI Tutorial

Phase 1: Research — /task-research

/task-research topic="Frontend coverage gaps — run coverage report for src/dataviewer/frontend/src/, identify all files below 80% coverage not already covered by issues #214-#221, categorize by component type"

Phase 2: Plan — /task-plan

/task-plan research="{research-output}/remaining-component-tests.md"

Phase 3: Implement — /task-implement

/task-implement plan="{plan-output}/remaining-component-tests-plan.instructions.md"

Phase 4: Review — /task-review

/task-review plan="{plan-output}/remaining-component-tests-plan.instructions.md"

Review focus:

• Coverage thresholds met (80% lines, functions, branches, statements)
• No test files are empty or trivial (just rendering without assertions)
• Error boundary tests actually trigger error recovery
• No coverage gaps hidden by overly broad exclude patterns