Fix critical bugs from code review

- room.gd: Add signal tracking and explicit cleanup in _exit_tree
- room.gd: Guard _on_enemy_died against race condition after room freed
- player.gd: Set _shield_ready = false on shield activation
- player.gd: Fix coolant zone lambda syntax error
- player.gd: Add apply_knockback() method for Hivemind pulse
- player.gd: Fix coolant zone memory leak (use Timer child)
- hud.gd: Remove deprecated boss bar code

project.godot

@@ -21,11 +21,16 @@ config/icon="res://assets/icon.svg"
 
 [autoload]
 
+# ===== AUTOLOAD INITIALIZATION ORDER =====
+# Order is critical! Dependencies must load before dependents.
+# Layer 0: Event system (no dependencies)
 EventBus="*res://scripts/event_bus.gd"
+# Layer 1: Core managers (depend on EventBus only)
 GameManager="*res://scripts/game_manager.gd"
-RunManager="*res://scripts/run_manager.gd"
 SaveManager="*res://scripts/save_manager.gd"
 UpgradeManager="*res://scripts/upgrades/upgrade_manager.gd"
+# Layer 2: Run systems (depend on Layer 1)
+RunManager="*res://scripts/run_manager.gd"
 CardCollection="*res://scripts/cards/card_collection.gd"
 NPCManager="*res://scripts/npcs/npc_manager.gd"
 LoreManager="*res://scripts/lore/lore_manager.gd"