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/mapUtils.ts

@@ -0,0 +1,104 @@
+/**
+ * Pure data-transform utilities for the map view (M2-T09).
+ * No leaflet imports — these functions are unit-testable in jsdom.
+ */
+
+import type { LocationRecord, PooRecord } from '../records'
+
+/** A heat point for L.heatLayer: [lat, lng, intensity]. */
+export type HeatPoint = [number, number, number]
+
+/** Map point with attached source record for click-to-edit. */
+export interface LocationMapPoint {
+  lat: number
+  lng: number
+  record: LocationRecord
+}
+
+export interface PooMapPoint {
+  lat: number
+  lng: number
+  record: PooRecord
+}
+
+// ---------------------------------------------------------------------------
+// Transforms
+// ---------------------------------------------------------------------------
+
+/**
+ * Convert location records to heat points.
+ * All points get intensity=1; callers can adjust if needed.
+ */
+export function locationsToHeatPoints(records: LocationRecord[]): HeatPoint[] {
+  return records.map((r) => [r.latitude, r.longitude, 1])
+}
+
+/**
+ * Convert poo records to heat points.
+ */
+export function pooToHeatPoints(records: PooRecord[]): HeatPoint[] {
+  return records.map((r) => [r.latitude, r.longitude, 1])
+}
+
+/**
+ * Convert location records to map points (for scatter layer).
+ */
+export function locationsToMapPoints(records: LocationRecord[]): LocationMapPoint[] {
+  return records.map((r) => ({ lat: r.latitude, lng: r.longitude, record: r }))
+}
+
+/**
+ * Convert poo records to map points (for scatter layer).
+ */
+export function pooToMapPoints(records: PooRecord[]): PooMapPoint[] {
+  return records.map((r) => ({ lat: r.latitude, lng: r.longitude, record: r }))
+}
+
+// ---------------------------------------------------------------------------
+// Client-side time-window filter (for poo records — the endpoint has no server filter)
+// ---------------------------------------------------------------------------
+
+/**
+ * Filter poo records to those whose timestamp falls within [start, end] (inclusive).
+ * start and end are ISO8601 strings (e.g. "2026-01-01T00:00:00Z").
+ * If start or end is null, that bound is open (no filtering on that side).
+ */
+export function filterPooByTimeWindow(
+  records: PooRecord[],
+  start: string | null,
+  end: string | null,
+): PooRecord[] {
+  if (!start && !end) return records
+  return records.filter((r) => {
+    const ts = r.timestamp
+    if (start && ts < start) return false
+    if (end && ts > end) return false
+    return true
+  })
+}
+
+// ---------------------------------------------------------------------------
+// Default time window helpers
+// ---------------------------------------------------------------------------
+
+/** Returns ISO8601 string for N days ago from now (UTC). */
+export function daysAgoISO(days: number): string {
+  const d = new Date()
+  d.setUTCDate(d.getUTCDate() - days)
+  return d.toISOString()
+}
+
+/** Returns ISO8601 string for now (UTC). */
+export function nowISO(): string {
+  return new Date().toISOString()
+}
+
+/** Compute a bounding center from an array of lat/lng points. Returns null if empty. */
+export function computeCenter(
+  points: Array<{ lat: number; lng: number }>,
+): [number, number] | null {
+  if (points.length === 0) return null
+  const sumLat = points.reduce((s, p) => s + p.lat, 0)
+  const sumLng = points.reduce((s, p) => s + p.lng, 0)
+  return [sumLat / points.length, sumLng / points.length]
+}