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/PersonTalkTest.php

@@ -639,4 +639,50 @@ class PersonTalkTest extends TestCase
         $this->assertLessThanOrEqual(68, $character->ai_age);
         $this->assertContains($character->ai_personality, Character::AI_PERSONALITIES);
     }
+
+    /**
+     * When the resolved primary model fails, the call retries with
+     * AI_FALLBACK_MODEL (owner-approved xiaomi/mimo-v2.6-flash).
+     */
+    public function test_person_talk_retries_with_fallback_model(): void
+    {
+        config([
+            'ai.openrouter.api_key' => 'test-key',
+            'ai.models' => ['openrouter/free'],
+            'ai.character_models' => [],
+        ]);
+
+        Http::fake([
+            'openrouter.ai/*' => Http::sequence()
+                ->push(['message' => 'Model overloaded'], 503)
+                ->push(['choices' => [['message' => ['content' => 'Tudo bem por aqui!']]]], 200),
+        ]);
+
+        [$userA, $me] = $this->makeCitizen();
+        [, $them] = $this->makeCitizen(); // silent peer → AI reply path
+
+        $this->actingAs($userA)
+            ->postJson('/talk/person', [
+                'kind' => 'character',
+                'peer' => $them->id,
+                'message' => 'Alô?',
+            ])
+            ->assertCreated();
+
+        $reply = PersonTalk::query()
+            ->where('from_character_id', $them->id)
+            ->where('is_fallback', false)
+            ->orderByDesc('id')
+            ->first();
+        $this->assertNotNull($reply);
+        $this->assertSame('Tudo bem por aqui!', $reply->body);
+
+        $models = [];
+        Http::assertSent(function ($request) use (&$models): bool {
+            $models[] = $request['model'];
+
+            return true;
+        });
+        $this->assertSame(['openrouter/free', 'xiaomi/mimo-v2.6-flash'], $models);
+    }
 }