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.

resources/views/city/viewer.blade.php

@@ -368,6 +368,12 @@
             beachStart: @json(__('city.beach_start')),
             beachPrompt: @json(__('city.beach_prompt')),
             beachActive: @json(__('city.beach_active')),
+            signPlaza: @json(__('city.sign_plaza')),
+            signBeach: @json(__('city.sign_beach')),
+            signFood: @json(__('city.sign_food')),
+            signHospital: @json(__('city.sign_hospital')),
+            signSchool: @json(__('city.sign_school')),
+            signCityhall: @json(__('city.sign_cityhall')),
             exerciseStopHint: @json(__('city.exercise_stopHint')),
             exerciseStart: @json(__('city.exerciseStart')),
             exerciseStop: @json(__('city.exerciseStop')),