Rename picture-targets to output-targets across entire codebase

Rename all Python modules, classes, API endpoints, config keys, frontend
fetch URLs, and Home Assistant integration URLs from picture-targets to
output-targets. Store loads both new and legacy JSON keys for backward
compatibility with existing data files.

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

custom_components/wled_screen_controller/ws_manager.py

@@ -40,7 +40,7 @@ class KeyColorsWebSocketManager:
         ws_base = self._server_url.replace("http://", "ws://").replace(
             "https://", "wss://"
         )
-        return f"{ws_base}/api/v1/picture-targets/{target_id}/ws?token={self._api_key}"
+        return f"{ws_base}/api/v1/output-targets/{target_id}/ws?token={self._api_key}"
 
     async def start_listening(self, target_id: str) -> None:
         """Start WebSocket connection for a target."""