feat(city): add airports, ATC agent, luminous signs, and AI model fallback chain

- Add two airports (north/south) with full geometry: runways, taxiways,
  aprons, terminals, hangars, stands, and helipads; walkable airport
  grounds extend beyond city bounds.
- Introduce ATC AI agent ("Torre de Controle City10") using AI_ATC_MODEL
  to generate takeoff clearances; includes dispatch endpoint with
  30-second cooldown and deterministic fallback on failure.
- Implement AI model fallback chain: preferred model → AI_FALLBACK_MODEL
  before failing, applied in ChatController and PersonTalkController.
- Add luminous sign labels (letreiros) for plazas, beach, food, hospital,
  school, city hall, and airports with day/night glow.
- Fix city presence cache: compute is_me per viewer instead of baking
  into shared per-second cache to prevent cross-user flag leakage.
- Add tests: AirportTest, CityPresenceTest, SignLabelsTest, and
  PersonTalkTest fallback model retry scenario.

routes/web.php

@@ -129,6 +129,14 @@ Route::middleware('auth')->group(function (): void {
         Route::post('/talk/person', [PersonTalkController::class, 'send'])
             ->middleware('throttle:30,1')
             ->name('talk.person.send');
+
+        // Airport ops: site info + ATC clearances (AI_ATC_MODEL).
+        Route::get('/city/airport', [CityViewerController::class, 'airport'])
+            ->middleware('throttle:60,1')
+            ->name('city.airport');
+        Route::post('/city/airport/dispatch', [CityViewerController::class, 'dispatch'])
+            ->middleware('throttle:60,1')
+            ->name('city.airport.dispatch');
     });
 });