Add audio-reactive color strip sources, improve delete error messages

Add new "audio" color strip source type with three visualization modes
(spectrum analyzer, beat pulse, VU meter) supporting WASAPI loopback and
microphone input via PyAudioWPatch. Includes shared audio capture with
ref counting, real-time FFT spectrum analysis, and beat detection.

Improve all referential integrity 409 error messages across delete
endpoints to include specific names of referencing entities instead of
generic "one or more" messages.

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

server/src/wled_controller/api/routes/picture_sources.py

@@ -263,10 +263,12 @@ async def delete_picture_source(
     """Delete a picture source."""
     try:
         # Check if any target references this stream
-        if store.is_referenced_by_target(stream_id, target_store):
+        target_names = store.get_targets_referencing(stream_id, target_store)
+        if target_names:
+            names = ", ".join(target_names)
             raise HTTPException(
                 status_code=409,
-                detail="Cannot delete picture source: it is assigned to one or more targets. "
+                detail=f"Cannot delete picture source: it is assigned to target(s): {names}. "
                        "Please reassign those targets before deleting.",
             )
         store.delete_stream(stream_id)