Quaternius weapons, input fixes, sound & path fixes

- Added 6 Quaternius weapon models (Pistol, Revolver, Rifle, Shotgun, P90, SniperRifle)
- Created weapon resource files with balanced stats
- Wired Pistol + Rifle into player.tscn replacing Kenney blasters
- Fixed WASD input (matched input map action names)
- Fixed Escape key toggles mouse capture
- Added Audio autoload singleton
- Fixed broken sound asset paths across all scripts
- Fixed all scene ext_resource text paths (nested under assets/kenney-fps/)
- Fixed all .import source_file paths
- Deleted stale .import files (will be regenerated by editor on open)

examples/shared/scripts/lan-bootstrapper.gd

@@ -83,7 +83,7 @@ func _ensure_input_focus() -> void:
 	## Force the game window to have keyboard focus and captured mouse.
 	## On Windows GUI exports, the window may not hold keyboard focus after
 	## the connection UI is dismissed, causing Input.get_axis() to return 0.
-	OS.move_to_foreground()
+	DisplayServer.window_move_to_foreground()
 	Input.set_mouse_mode(Input.MOUSE_MODE_CAPTURED)
 	# Deferred retry after window settles
 	get_window().call_deferred("grab_focus")