feat(#254,#114): custom POI UI + score breakdown stacked-bar viz
Task A (#254): Leaflet click-to-add custom POIs
- sessionId.ts: getOrCreateSessionId() from localStorage
- types/customPoi.ts: CustomPoi, CustomPoiCreate, CustomPoiUpdate
- hooks/useCustomPois.ts: useCustomPois / useAddCustomPoi / useUpdateCustomPoi / useDeleteCustomPoi (TanStack Query, X-Session-Id header)
- CustomPoiLayer.tsx: LayerGroup with CircleMarker (green/red/gray by weight), popup with edit/delete
- CustomPoiToggleButton.tsx: crosshair mode toggle button
- CustomPoiAddModal.tsx: modal form (name, 26 categories, weight -5..+5, notes)
- CustomPoiEditModal.tsx: same form for editing existing POI
- SiteMap.tsx: MapClickHandler (useMapEvents), integrated all custom POI components
- page.tsx: useCustomPois hook + passes customPois + parcelCad to SiteMap
Task B (#114): ScoreBreakdownStackedBar
- ScoreBreakdownStackedBar.tsx: horizontal stacked bar by category with positive/negative split, toggle between category and factor views, custom POIs highlighted orange with dashed outline
- OverviewTab.tsx: renders ScoreBreakdownStackedBar below ScoreBreakdownPanel
Requires backend PR with /api/v1/custom-pois endpoints merged before POI CRUD works.
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