feat: task 2.1 MapView singleton + mapReady gate

- pnpm add maplibre-gl + -D @types/geojson.
- src/map/core/styles.ts: defaultStyle (OSM raster bootstrap; 2.2
  replaces with the basemap-switcher descriptor table).
- src/map/core/map-view.tsx: module-level Map singleton lazily created
  on first <MapView> mount, attached to a class="trm-map-host" detached
  <div> that React refs append/remove on mount/unmount. Style-data
  lifecycle flips mapReady false on every styledata event, polls
  loaded() at 33ms intervals, flips ready true once the style is
  loaded — the canonical MapLibre style-swap dance.
- Exports getMap()/getMapReady()/subscribeMapReady()/useMapReady (via
  useSyncExternalStore for SSR-safe + concurrent-safe reads). getMap()
  throws if called pre-mount; the explicit failure mode beats a
  null-able top-level export.
- src/routes/_authed/monitor.tsx: new /monitor route, full-viewport
  <MapView /> for 2.1 (no children — subsequent tasks plug in here).
- src/routes/_authed/index.tsx: home-page card now links to /monitor.
- eslint.config.js: override for src/map/** + src/live/** disables
  react-refresh/only-export-components. Same pattern as the existing
  overrides for shadcn primitives and route files.

Deviation: spec sketched a top-level `map` constant export; implemented
as `getMap(): MapLibreMap` (a function) so the singleton stays lazy
until <MapView> mounts. Top-level constant would either force eager
init (breaks SSR/tests) or be nullable (footgun). The function form
throws a clear error if called pre-mount.

Bundle: /monitor lazy chunk is 1MB raw / 274KB gzipped (MapLibre + CSS).
Other routes unaffected. Vite chunk-size warning is harmless.

.planning/phase-2-live-map/02-tile-source-switcher.md

@@ -19,7 +19,7 @@ After this task, a small floating control on the map lets operators pick the bas
     id: 'esri-satellite' | 'opentopo' | 'osm' | 'google-satellite';
     label: string;
     style: maplibregl.StyleSpecification | string; // inline raster style or URL
-    available: (cfg: RuntimeConfig) => boolean;     // gates Google on googleMapsKey
+    available: (cfg: RuntimeConfig) => boolean; // gates Google on googleMapsKey
     attribution: string;
   };
   ```
@@ -74,7 +74,9 @@ export const BASEMAP_STYLES: BasemapDescriptor[] = [
     id: 'esri-satellite',
     label: 'Satellite',
     style: styleCustom({
-      tiles: ['https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}'],
+      tiles: [
+        'https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}',
+      ],
       attribution: 'Tiles © Esri',
       maxZoom: 19,
     }),