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

test/unit/authSkipPaths.spec.js

@@ -10,6 +10,7 @@ describe('authSkipPaths', () => {
   it('does not skip any protected path', () => {
     const protectedPaths = [
       ...PROTECTED_PATH_PREFIXES,
+      '/api/alpr',
       '/api/cameras',
       '/api/devices',
       '/api/devices/any-id',