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/05-map-positions.md

@@ -215,8 +215,8 @@ function buildPositionFeature(p: PositionEntry, device?: Device): Feature {
 
 function inferStatus(p: PositionEntry): 'success' | 'error' | 'neutral' | 'info' {
   // Phase 2 heuristic — refine in Phase 3.4 with real domain rules.
-  if ((p.speed ?? 0) > 1) return 'success';     // moving
-  return 'neutral';                              // stopped / idle
+  if ((p.speed ?? 0) > 1) return 'success'; // moving
+  return 'neutral'; // stopped / idle
 }
 ```
 
@@ -228,9 +228,9 @@ Phase 2's status inference is a placeholder; Phase 3.4 (per-device detail) will
 // In src/routes/_authed/monitor.tsx
 <MapView>
   <MapPositions />
-  <MapTrails />            {/* 2.6 */}
-  <MapDefaultCamera />     {/* 2.8 */}
-  <MapSelectedDevice />    {/* 2.8 */}
+  <MapTrails /> {/* 2.6 */}
+  <MapDefaultCamera /> {/* 2.8 */}
+  <MapSelectedDevice /> {/* 2.8 */}
 </MapView>
 ```