feat(KB-048): add collapsible list sections to dashboard

- Add section expansion state management with localStorage persistence
- Update section headers with chevron toggle controls
- Implement conditional task row rendering based on section state
- Add Expand All / Collapse All toolbar controls
- Add CSS styles for chevron rotation animation and section headers
- Add comprehensive tests for collapsible section behavior

.changeset/collapsible-list-sections.md

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+"@dustinbyrne/kb": minor
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+Add collapsible column sections to List View. Each column group (triage, todo, in-progress, in-review, done) can now be independently expanded or collapsed by clicking the section header. Section expansion state is persisted to localStorage and restored on page reload. Includes expand all / collapse all buttons in the toolbar for quick access.