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

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

server/plugins/cot.js

@@ -108,7 +108,7 @@ async function processFrame(socket, rawMessage, payload, authenticated) {
       socket.destroy()
       return
     }
-    updateFromCot(parsed).catch((err) => {
+    updateFromCot({ ...parsed, type: parsed.eventType }).catch((err) => {
       console.error('[cot] Error updating from CoT:', err?.message)
     })
     if (authenticated) broadcast(socket, rawMessage)