fix(core): remove class_name from autoload scripts to prevent singleton conflict

Godot 4 throws "Class hides an autoload singleton" when a script declares
class_name with the same name as its registered autoload. Removed class_name
from AudioManager and RoomNavigator — both are accessible globally via their
autoload name without it. Also ignores Godot-generated *.uid files.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -3,6 +3,7 @@
 # Godot generated files
 .godot/
 .import/
+*.uid
 
 # Godot-specific ignores
 export.cfg

scripts/autoload/AudioManager.gd

@@ -1,5 +1,5 @@
 ## AudioManager — music playback with cross-fade, SFX playback, volume control.
-class_name AudioManager extends Node
+extends Node
 
 const DEFAULT_MUSIC_VOLUME: float = 0.6
 const CROSSFADE_DURATION: float = 1.0

scripts/systems/room_navigator.gd

@@ -1,5 +1,5 @@
 ## RoomNavigator — autoload that moves the Camera2D smoothly between hospital floors.
-class_name RoomNavigator extends Node
+extends Node
 
 signal room_changed(floor_index: int)