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/constants.js

@@ -2,10 +2,22 @@
  * Application constants with environment variable support.
  */
 
+// CoT / tracking (fixed defaults — not env-configurable)
+export const COT_TTL_MS = 90_000
+/** @deprecated Use COT_TTL_MS */
+export const COT_ENTITY_TTL_MS = COT_TTL_MS
+export const COT_OSINT_TTL_MS = 30_000
+export const COT_PRUNE_INTERVAL_MS = 15_000
+export const COT_SSE_HEARTBEAT_MS = 15_000
+export const OPENSKY_CACHE_MS = 5_000
+export const TRACKING_FEED_DEBOUNCE_MS = 500
+export const COT_TAK_FILTER_BBOX = false
+export const COT_SSE_MAX_ENTITIES = 2000
+export const MAX_OPENSKY_BBOX_DEGREES = 10
+
 // Timeouts (milliseconds)
 export const COT_AUTH_TIMEOUT_MS = Number(process.env.COT_AUTH_TIMEOUT_MS) || 15_000
 export const LIVE_SESSION_TTL_MS = Number(process.env.LIVE_SESSION_TTL_MS) || 60_000
-export const COT_ENTITY_TTL_MS = Number(process.env.COT_ENTITY_TTL_MS) || 90_000
 export const POLL_INTERVAL_MS = Number(process.env.POLL_INTERVAL_MS) || 1500
 export const SHUTDOWN_TIMEOUT_MS = Number(process.env.SHUTDOWN_TIMEOUT_MS) || 30_000