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/api/alpr.get.js

@@ -0,0 +1,19 @@
+import { getDb } from '../utils/db.js'
+import { requireAuth } from '../utils/authHelpers.js'
+import { getAlprCameras, parseBbox } from '../utils/alpr.js'
+
+export default defineEventHandler(async (event) => {
+  requireAuth(event)
+  let bbox
+  try {
+    bbox = parseBbox(getQuery(event))
+  }
+  catch (error) {
+    throw createError({
+      statusCode: error?.statusCode || 400,
+      message: error?.message || 'invalid bbox',
+    })
+  }
+  const db = await getDb()
+  return getAlprCameras(db, bbox)
+})