M2-T09: build data visualization UI (heatmap map as home page)

- self-contained RecordsMap (only module importing leaflet/react-leaflet/
  leaflet.heat/leaflet.markercluster); OSM tiles, swappable behind clean props
- heatmap layers for location + poo (primary); time-range selector fetches
  only the window (locations server-filtered; poo client-filtered)
- toggleable scatter layer with marker clustering; point-select reuses T10's
  edit/delete modals + hooks; query-key prefixes refresh map on mutation
- pure map logic isolated + unit-tested; leaflet mocked in component tests
- responsive layout; typed client only

frontend/src/map/index.ts

@@ -0,0 +1,18 @@
+/**
+ * Public surface of the map module (M2-T09).
+ * Only RecordsMap.tsx imports leaflet — external code should not.
+ */
+export { RecordsMap } from './RecordsMap'
+export type { RecordsMapProps } from './RecordsMap'
+
+export {
+  locationsToHeatPoints,
+  pooToHeatPoints,
+  locationsToMapPoints,
+  pooToMapPoints,
+  filterPooByTimeWindow,
+  daysAgoISO,
+  nowISO,
+  computeCenter,
+} from './mapUtils'
+export type { HeatPoint, LocationMapPoint, PooMapPoint } from './mapUtils'