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

app/components/AppShell.vue

@@ -26,6 +26,11 @@
           :user="user"
           @signout="onLogout"
         />
+        <span
+          v-else-if="authPending"
+          class="inline-block h-8 w-8"
+          aria-hidden="true"
+        />
         <NuxtLink
           v-else
           to="/login"
@@ -75,7 +80,7 @@ watch(sidebarCollapsed, (v) => {
   }
 })
 
-const { user, refresh } = useUser()
+const { user, authPending, refresh } = useUser()
 
 watch(isMobile, (mobile) => {
   if (mobile) drawerOpen.value = false