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

server/utils/cotSnapshot.js

@@ -0,0 +1,15 @@
+import {
+  COT_OSINT_TTL_MS,
+  COT_SSE_MAX_ENTITIES,
+  COT_TAK_FILTER_BBOX,
+  COT_TTL_MS,
+} from './constants.js'
+
+export function getCotSnapshotOpts() {
+  return {
+    ttlMs: COT_TTL_MS,
+    osintTtlMs: COT_OSINT_TTL_MS,
+    takFilterBbox: COT_TAK_FILTER_BBOX,
+    maxEntities: COT_SSE_MAX_ENTITIES,
+  }
+}