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.

config/ai.php

@@ -84,6 +84,9 @@ return [
         'nvidia/nemotron-3.5-lightning:free',
         'liquid/lfm-2.5-2.6b:free',
         'openrouter/free',
+        // Owner-approved exception: paid but near-zero cost
+        // (1.4e-7/1k tokens), verified live on 2026-11-01.
+        'xiaomi/mimo-v2.6-flash',
     ],
 
     /*
@@ -115,6 +118,31 @@ return [
 
     'character_models' => $parseCharacterModels((string) env('AI_CHARACTER_MODELS', '')),
 
+    /*
+    |--------------------------------------------------------------------------
+    | Air Traffic Control Model (AI_ATC_MODEL)
+    |--------------------------------------------------------------------------
+    |
+    | Default model used by the airport control tower agent for movement
+    | clearances (takeoff authorizations). Must stay inside allowed_models.
+    |
+    */
+
+    'atc_model' => env('AI_ATC_MODEL', 'poolside/laguna-xs-2.1:free'),
+
+    /*
+    |--------------------------------------------------------------------------
+    | Fallback Model (AI_FALLBACK_MODEL)
+    |--------------------------------------------------------------------------
+    |
+    | Tried whenever the preferred model of a call fails (chain fallback).
+    | Owner-approved paid model with near-zero cost; must stay inside
+    | allowed_models.
+    |
+    */
+
+    'fallback_model' => env('AI_FALLBACK_MODEL', 'xiaomi/mimo-v2.6-flash'),
+
     /*
     |--------------------------------------------------------------------------
     | Default Model