Add side panels, task selection, graph animation, and project docs

- Foldable left panel (user profile) and right panel (task details)
- Clicking a task in the list or graph node selects it and shows details
- Both views (task list + graph) always mounted via absolute inset-0 for
  correct canvas dimensions; tabs toggle visibility with opacity
- Graph node selection animation: other nodes repel outward (charge -600),
  then selected node smoothly slides to center (500ms cubic ease-out),
  then charge restores to -120 and graph stabilizes
- Graph re-fits on tab switch and panel resize via ResizeObserver
- Fix UUID string IDs throughout (backend returns UUIDs, not integers)
- Add TaskDetailPanel, UserPanel components
- Add CLAUDE.md project documentation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/target/release/.fingerprint/ppv-lite86-bd9908ddae3695d8/invoked.timestamp

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backend/target/release/.fingerprint/ppv-lite86-bd9908ddae3695d8/lib-ppv_lite86

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+1e9e4cd87563412e

backend/target/release/.fingerprint/ppv-lite86-bd9908ddae3695d8/lib-ppv_lite86.json

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