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/config_flow.py

@@ -61,7 +61,7 @@ async def validate_server(
     headers = {"Authorization": f"Bearer {api_key}"}
     try:
         async with session.get(
-            f"{server_url}/api/v1/picture-targets",
+            f"{server_url}/api/v1/output-targets",
             headers=headers,
             timeout=timeout,
         ) as resp: