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/composables/useCotLayers.js

@@ -0,0 +1,48 @@
+const STORAGE_KEY = 'kestrel-cot-layers'
+
+const DEFAULT_LAYERS = Object.freeze({ air: true, surface: true, ground: true })
+
+function loadLayers() {
+  if (typeof localStorage === 'undefined') return { ...DEFAULT_LAYERS }
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY)
+    if (!raw) return { ...DEFAULT_LAYERS }
+    const parsed = JSON.parse(raw)
+    return {
+      air: parsed.air !== false,
+      surface: parsed.surface !== false,
+      ground: parsed.ground !== false,
+    }
+  }
+  catch {
+    return { ...DEFAULT_LAYERS }
+  }
+}
+
+function saveLayers(layers) {
+  if (typeof localStorage === 'undefined') return
+  try {
+    localStorage.setItem(STORAGE_KEY, JSON.stringify(layers))
+  }
+  catch { /* ignore quota */ }
+}
+
+export function useCotLayers() {
+  const layers = ref(loadLayers())
+
+  const layerQuery = computed(() => {
+    const parts = []
+    if (layers.value.air) parts.push('air')
+    if (layers.value.surface) parts.push('surface')
+    if (layers.value.ground) parts.push('ground')
+    return parts.length ? parts.join(',') : 'none'
+  })
+
+  function toggleLayer(name) {
+    if (!(name in DEFAULT_LAYERS)) return
+    layers.value = { ...layers.value, [name]: !layers.value[name] }
+    saveLayers(layers.value)
+  }
+
+  return Object.freeze({ layers, layerQuery, toggleLayer })
+}