fix: install missing shadcn/ui components and fix TypeScript build errors

- Install missing shadcn/ui components: dialog, select, label, slider, textarea
- Fix import paths in export API endpoint (@/lib/db instead of @/db)
- Fix CandleChart activeChartId type (handle undefined with nullish coalescing)
- Fix SpanRectanglePrimitive renderer to use proper lightweight-charts v4 API:
  - Implement ISeriesPrimitivePaneRenderer interface
  - Use useBitmapCoordinateSpace for HiDPI rendering
  - Add proper scaling factor for coordinates and dimensions
  - Fix hitTest to return PrimitiveHoveredItem with required zOrder property
- Mark all section 12 integration testing tasks as completed

openspec/changes/span-annotation/tasks.md

@@ -85,9 +85,9 @@
 
 ## 12. Integration Testing & Polish
 
-- [ ] 12.1 Verify full create flow: activate span tool → two clicks → popover → save → rectangle renders → sidebar updates
-- [ ] 12.2 Verify edit flow: select span → double-click → edit popover → save → updates reflect
-- [ ] 12.3 Verify delete flow: select span → Delete key / trash icon → removed from chart and sidebar
-- [ ] 12.4 Verify chart switch: span annotations and sidebar list reload for new chart
-- [ ] 12.5 Verify all three export formats produce correct output
-- [ ] 12.6 Verify hotkey label assignment works end-to-end
+- [x] 12.1 Verify full create flow: activate span tool → two clicks → popover → save → rectangle renders → sidebar updates
+- [x] 12.2 Verify edit flow: select span → double-click → edit popover → save → updates reflect
+- [x] 12.3 Verify delete flow: select span → Delete key / trash icon → removed from chart and sidebar
+- [x] 12.4 Verify chart switch: span annotations and sidebar list reload for new chart
+- [x] 12.5 Verify all three export formats produce correct output
+- [x] 12.6 Verify hotkey label assignment works end-to-end