feat(city-defense): city bombard retaliation + building HP bonuses

- City bombard: melee attackers take 5-30 damage based on city population
  and castle bombard bonus (city_str = pop*3 + castle bonus)
- Building HP bonuses: when walls/castle complete, increase city max_hp
  and heal by hp_bonus value from building data
- Castle data: added city_bombard_strength: 12, city_bombard_range: 2

Combined with prior commit's city healing (20 HP/turn) and tiered wall
penalties (walls=0.75x, castle=0.60x), cities now require sustained
multi-turn sieges instead of 1-2 turn captures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/resources/buildings/defense_special.json

@@ -91,6 +91,14 @@
         "type": "ranged_defense",
         "value": 8,
         "scope": "city"
+      },
+      {
+        "type": "city_bombard_strength",
+        "value": 12
+      },
+      {
+        "type": "city_bombard_range",
+        "value": 2
       }
     ],
     "requires_building": "walls",

src/game/engine/src/modules/combat/combat_resolver.gd

@@ -143,6 +143,16 @@ func _apply_resolve_results(
 		if infusion_system != null:
 			infusion_system.on_unit_killed(defender)
 
+	# City bombard retaliation: city deals damage to melee attackers
+	if defender is CityScript and not attacker_killed:
+		var bombard_dmg: int = _compute_city_bombard(defender, attacker)
+		if bombard_dmg > 0:
+			attacker.hp = maxi(0, attacker.hp - bombard_dmg)
+			result["city_bombard_damage"] = bombard_dmg
+			if attacker.hp <= 0:
+				attacker_killed = true
+				CombatUtilsScript.handle_unit_death(attacker, defender, all_units)
+
 	if result.get("captured", false) and defender is CityScript:
 		CombatUtilsScript.capture_city(defender, attacker, defender.owner, all_units)
 
@@ -307,6 +317,24 @@ func _count_flanking(attacker: RefCounted, near_def: Array) -> int:
 
 
 ## Terrain defense bonus from the tile the unit stands on.
+## Compute city bombard retaliation damage.
+## City strength = population * 3 + building bombard bonuses.
+## Damage = 15 * (city_strength / attacker_strength), clamped [5, 30].
+func _compute_city_bombard(city: RefCounted, attacker: RefCounted) -> int:
+	var city_str: float = float(city.population) * 3.0
+	# Add castle bombard bonus if present
+	if city.has_building("castle"):
+		var bdata: Dictionary = DataLoader.get_building("castle")
+		for effect: Dictionary in bdata.get("effects", []):
+			if effect.get("type", "") == "city_bombard_strength":
+				city_str += float(effect.get("value", 0))
+	if city_str <= 0.0:
+		return 0
+	var atk_str: float = float(attacker.attack) if attacker is UnitScript else 10.0
+	var ratio: float = city_str / maxf(atk_str, 1.0)
+	return clampi(roundi(15.0 * ratio), 5, 30)
+
+
 func _get_terrain_defense(unit: RefCounted, game_map: RefCounted) -> int:
 	if game_map == null:
 		return 0

src/game/engine/src/modules/management/turn_processor.gd

@@ -88,6 +88,7 @@ func _process_production(player: RefCounted) -> void:  # Player
 				EventBus.city_unit_completed.emit(city_ref, unit)
 		elif item_type == "building":
 			c.add_building(item_id)
+			_apply_building_bonuses(c, item_id)
 			EventBus.city_building_completed.emit(city_ref, item_id)
 		elif item_type == "item":
 			var i_data: Dictionary = DataLoader.get_item(item_id)
@@ -211,6 +212,17 @@ func _process_growth(player: RefCounted) -> void:  # Player
 		c.process_growth(tile_json)
 
 
+func _apply_building_bonuses(city: CityScript, building_id: String) -> void:
+	var bdata: Dictionary = DataLoader.get_building(building_id)
+	var effects: Array = bdata.get("effects", [])
+	for effect: Dictionary in effects:
+		var etype: String = effect.get("type", "")
+		var value: int = int(effect.get("value", 0))
+		if etype == "hp_bonus" and value > 0:
+			city.set_max_hp(city.max_hp + value)
+			city.heal(value)
+
+
 func _process_city_healing(player: RefCounted) -> void:
 	for city_ref: Variant in player.cities:
 		if city_ref is CityScript: