Add ADS-B, AIS, and ALPR map layers with live CoT streaming (#36)

## Summary

- **ADS-B & AIS:** OpenSky and AISStream OSINT feeds upsert into the CoT store; tactical tracks still arrive via adsbcot/aiscot on `:8089`. Map clients subscribe via `GET /api/cot/stream` (SSE) with viewport bbox filtering and Air / Surface / Team layer toggles.
- **ALPR (Flock/OSM):** Toggleable license-plate reader layer sourced from OpenStreetMap, with SQLite cache, Overpass fallback, tiled viewport fetching, and clustered markers with direction cones.
- **Map performance:** Ring-based tile selection (fixes zoom-out crash), immutable tile cache, incremental marker sync, split cluster load/query, and padded SSE bbox to reduce reconnect churn.

## Docs

- `docs/tracking.md` — ADS-B/AIS accuracy tiers, freshness, self-hosted receivers, optional OSINT API keys
- `docs/map-and-cameras.md` — ALPR layer and map behavior updates

---------

Co-authored-by: Madison Grubb <madison@elastiflow.com>
Reviewed-on: #36

app/utils/mapMarkerSync.js

@@ -0,0 +1,37 @@
+const SYNC_KEY = '_kestrelMarkerSync'
+
+const pointFeatures = (features, keyFor) => (features ?? [])
+  .filter(f => f?.geometry?.type === 'Point')
+  .map(f => ({ feature: f, key: keyFor(f) }))
+  .filter(({ key }) => key != null)
+
+export function syncFeatureMarkers(layer, features, { keyFor, create, update }) {
+  const prev = layer[SYNC_KEY] ?? new Map()
+  const next = pointFeatures(features, keyFor).reduce((map, { feature, key }) => {
+    const existing = prev.get(key)
+    if (existing) {
+      update(existing, feature)
+      return new Map([...map, [key, existing]])
+    }
+    const marker = create(feature)
+    layer.addLayer(marker)
+    return new Map([...map, [key, marker]])
+  }, new Map())
+
+  Array.from(prev.entries())
+    .filter(([key]) => !next.has(key))
+    .forEach(([, marker]) => layer.removeLayer(marker))
+
+  layer[SYNC_KEY] = next
+}
+
+export function clearFeatureMarkers(layer) {
+  if (!layer) return
+  const prev = layer[SYNC_KEY]
+  if (prev) {
+    Array.from(prev.values()).forEach(marker => layer.removeLayer(marker))
+    layer[SYNC_KEY] = new Map()
+    return
+  }
+  layer.clearLayers()
+}