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

docs/map-and-cameras.md

@@ -5,6 +5,7 @@ KestrelOS shows a **map** with devices, POIs, live sessions (Share live), and AT
 ## Map Layers
 
 - **Devices** - Fixed feeds (IPTV, ALPR, CCTV, NVR, etc.) added via API
+- **ALPR (OSM / DeFlock)** - Crowdsourced license-plate cameras from OpenStreetMap; toggle on the map (camera icon control). Reference only, no stream.
 - **POIs** - Points of interest (admin/leader can edit)
 - **Live sessions** - Mobile devices streaming via Share live
 - **CoT (ATAK/iTAK)** - Amber markers for connected TAK devices (position only)
@@ -47,6 +48,15 @@ Stream URLs must be `http://` or `https://`.
 
 **Cameras endpoint:** `GET /api/cameras` returns devices + live sessions + CoT entities.
 
+## ALPR layer (DeFlock / OpenStreetMap)
+
+deflock.me has no bulk download API. KestrelOS queries OpenStreetMap via Overpass (`surveillance:type=ALPR`) and returns **GeoJSON FeatureCollection** from `GET /api/alpr`.
+
+- **Map:** ALPR layer is on by default (toggle top-left to hide). Marker popups show OSM identifying tags (manufacturer, model, operator, ref, Wikidata, etc.) when contributors tagged them.
+- **Offline:** Run `npm run import:alpr` to preload SQLite; cache serves automatically when Overpass is unreachable.
+
+Attribution: © OpenStreetMap contributors.
+
 ## POIs
 
 Admins/leaders add/edit from **POI** page (sidebar). POIs appear as map pins (reference only, no stream).