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/multiplayer-fps/scripts/player-spawner.gd

@@ -94,8 +94,9 @@ func _handle_new_peer(id: int):
 		if bomb:
 			bomb.sync_to_peer(id)
 		if avatars.size() <= 2:
-			# First opponent joined — restart round so both spawn alive
-			round_manager.start_round()
+			# Dedicated server handles match start via headless_server.gd
+			if not _dedicated_server:
+				round_manager.start_round()
 		else:
 			# 3+ players: sync state, spectate until next round
 			round_manager.sync_to_peer(id)