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/mapCluster.js

@@ -0,0 +1,31 @@
+import Supercluster from 'supercluster'
+
+export function createClusterIndex(options = {}) {
+  const index = new Supercluster(options)
+  const state = { features: Object.freeze([]) }
+
+  return {
+    load(features) {
+      const list = Object.freeze([...(features ?? [])])
+      index.load(list)
+      state.features = list
+    },
+    query(view) {
+      if (!view || state.features.length === 0) return []
+      const { west, south, east, north, zoom } = view
+      return index.getClusters(
+        [west, south, east, north],
+        Math.floor(zoom ?? 14),
+      ).map((feature) => {
+        if (!feature.properties?.cluster) return feature
+        return {
+          ...feature,
+          properties: {
+            ...feature.properties,
+            expansionZoom: index.getClusterExpansionZoom(feature.properties.cluster_id),
+          },
+        }
+      })
+    },
+  }
+}