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

scripts/import-alpr.js

@@ -0,0 +1,17 @@
+#!/usr/bin/env node
+import { getDb, closeDb } from '../server/utils/db.js'
+import { importAllAlprNodes } from '../server/utils/alpr.js'
+
+try {
+  const db = await getDb()
+  console.log('[import-alpr] Fetching ALPR nodes from Overpass…')
+  const count = await importAllAlprNodes(db)
+  console.log(`[import-alpr] Cached ${count} nodes in SQLite.`)
+}
+catch (error) {
+  console.error('[import-alpr] Failed:', error?.message || error)
+  process.exitCode = 1
+}
+finally {
+  closeDb()
+}