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

lang/en.json

@@ -192,7 +192,7 @@
     "city.citizens_near": "Citizens",
     "city.apply_job": "Apply for",
     "city.buy_hint": "Buys 1 food + 1 water + 10 materials",
-    "city.hospital_hit": "You were hit by a vehicle! Hospitalized for 2 days.",
+    "city.hospital_hit": "You were hit by a vehicle! Hospitalized for 1 hour.",
     "city.hospital_already": "You are already in the hospital.",
     "city.hospital_blocked": "You are hospitalized and cannot do that right now.",
     "city.hospital_bed": "Hospitalized",
@@ -204,5 +204,17 @@
     "city.vol_music": "Music",
     "city.vol_sfx": "Effects",
     "city.mute": "Mute",
-    "city.audio_hint": "Volume saved on this device."
+    "city.audio_hint": "Volume saved on this device.",
+    "city.hud_health": "Health",
+    "city.hud_exercise": "Workouts",
+    "city.exercise_use": "Press E to exercise",
+    "city.exercise_active": "Exercising",
+    "city.exercise_stopHint": "to stop",
+    "city.exercise_ok": "Nice! +2 health.",
+    "city.exercise_need_equipment": "Get closer to plaza gym equipment.",
+    "city.exercise_need_awake": "You must be awake to exercise.",
+    "city.exercise_tired": "You are too tired to exercise.",
+    "city.exercise_max_health": "Health is already at maximum!",
+    "city.exerciseStart": "Starting exercise…",
+    "city.exerciseStop": "Exercise stopped."
 }