feat(city): add plaza exercise system with health tracking

- Adds CityPlazas support class for deterministic public plaza generation with outdoor gym equipment
- Implements exercise and stop-exercise actions with proximity validation to equipment
- Introduces health (0-100) and exercise_count attributes to Character model
- Reduces hospital stay duration from two game days to one game hour
- Adds 3D gym equipment rendering (bench, bars, bike, treadmill) in city viewer
- Includes exercise state machine handling in world ticker with energy drain
- Adds comprehensive PlazaExerciseTest and updates HospitalAdmissionTest
- Provides localized UI strings for health HUD and exercise prompts

database/seeders/CityWorldSeeder.php

@@ -56,7 +56,7 @@ class CityWorldSeeder extends Seeder
             ['salary' => 14, 'requires_education' => 60],
         );
 
-        // City hospital: accident victims are admitted here for two game days.
+        // City hospital: accident victims are admitted here for one game hour.
         Building::updateOrCreate(
             [
                 'city_id' => $city->id,
@@ -83,5 +83,9 @@ class CityWorldSeeder extends Seeder
         User::query()->where('status', User::STATUS_ACTIVE)->each(function (User $user) use ($city): void {
             Character::ensureForUser($user, $city);
         });
+
+        // Backfill fitness columns for characters created before the migration.
+        Character::query()->whereNull('health')->update(['health' => 100]);
+        Character::query()->whereNull('exercise_count')->update(['exercise_count' => 0]);
     }
 }