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.

tests/Feature/SignLabelsTest.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Models\User;
+use Database\Seeders\CityWorldSeeder;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+/**
+ * Luminous-sign labels must exist in every locale (RULES.md 1.4:
+ * every user-visible string ships in pt_BR, en and es).
+ */
+class SignLabelsTest extends TestCase
+{
+    use RefreshDatabase;
+
+    /**
+     * Locales covered by the platform.
+     *
+     * @var list<string>
+     */
+    private const LOCALES = ['pt_BR', 'en', 'es'];
+
+    /**
+     * Sign label keys rendered by the 3D letreiros.
+     *
+     * @var list<string>
+     */
+    private const KEYS = [
+        'city.sign_plaza',
+        'city.sign_beach',
+        'city.sign_food',
+        'city.sign_hospital',
+        'city.sign_school',
+        'city.sign_cityhall',
+    ];
+
+    /**
+     * Every sign label exists (non-empty) in all three languages.
+     */
+    public function test_sign_labels_exist_in_all_locales(): void
+    {
+        foreach (self::LOCALES as $locale) {
+            $path = base_path("lang/{$locale}.json");
+            $this->assertFileExists($path);
+
+            $labels = json_decode((string) file_get_contents($path), true);
+            $this->assertIsArray($labels);
+
+            foreach (self::KEYS as $key) {
+                $this->assertArrayHasKey($key, $labels, "Missing {$key} in {$locale}");
+                $this->assertNotSame('', trim((string) $labels[$key]), "Empty {$key} in {$locale}");
+            }
+        }
+    }
+
+    /**
+     * The labels reach the viewer page for the active locale.
+     */
+    public function test_viewer_page_carries_sign_labels(): void
+    {
+        $this->seed(CityWorldSeeder::class);
+        $user = User::factory()->create([
+            'status' => User::STATUS_ACTIVE,
+            'is_active' => true,
+        ]);
+        $this->actingAs($user);
+
+        $html = $this->get('/city')->assertOk()->getContent();
+
+        foreach (['signPlaza', 'signBeach', 'signFood', 'signHospital', 'signSchool', 'signCityhall'] as $jsKey) {
+            $this->assertStringContainsString($jsKey.':', $html, "Missing i18n entry {$jsKey}");
+        }
+    }
+}