feat: task 2.5 MapPositions (clustered + selected sources)

- src/data/devices.ts: useDevicesById() — TanStack Query (5-min stale)
  returning Map<deviceId, Device>. deviceLabel() formats human-readable
  titles ("FMB920 #3458").
- src/map/layers/map-positions.tsx: <MapPositions /> side-effect-only.
  Two GeoJSON sources (clustered non-selected + unclustered selected).
  Five layers: non-selected symbol + direction + cluster-bubble,
  selected symbol + direction. Click handlers: marker -> selectDevice,
  cluster -> getClusterExpansionZoom + easeTo. Hover toggles cursor.
- src/routes/_authed/monitor.tsx: renders <MapPositions /> inside
  <MapView>.

Schema overhaul in src/auth/client.ts:
- Made Schema SDK-compatible. Each entry is an *array* of row types
  (devices: DeviceRow[], not just DeviceRow). RegularCollections<Schema>
  filters on array-like values; non-arrays collapse to never which
  broke readItems('devices', ...) with keyof Schema = never.
- Spelled out the composed client type as DirectusClient<Schema> &
  RestClient<Schema> & AuthenticationClient<Schema> — without the
  explicit annotation Schema didn't flow through .with(...) chain to
  request() call sites.
- Added DeviceRow + EventRow types; exported via @/auth.

useDevicesById uses readItems<Schema, 'devices', Query<Schema, DeviceRow>>
— explicit generics because the SDK doesn't infer Schema from the
receiver's type at call sites.

Deviations:
1. Spec referenced device.kind for category — Phase 1 schema doesn't
   have it yet; everything maps to 'default'. Refine when kind lands.
2. Cluster bubble uses 'default-neutral' sprite instead of a dedicated
   'cluster-background' (not in 2.3's registry). Swap in 3.8.
3. getClusterExpansionZoom is Promise-based in maplibre-gl 5.x (was
   callback-style); used .then().

Bundle: main bundle 394KB / 120KB gz, ~1KB up from 2.4. /monitor
chunk includes the new layer module (~10KB).

src/routes/_authed/monitor.tsx

@@ -1,6 +1,7 @@
 import { createFileRoute } from '@tanstack/react-router';
 import { BasemapSwitcher } from '@/map/core/basemap-switcher';
 import { MapView } from '@/map/core/map-view';
+import { MapPositions } from '@/map/layers/map-positions';
 
 export const Route = createFileRoute('/_authed/monitor')({
   component: MonitorPage,
@@ -22,6 +23,7 @@ function MonitorPage() {
           to <MapView>'s wrapper.
         */}
         <BasemapSwitcher />
+        <MapPositions />
       </MapView>
     </div>
   );