Filter audio devices by engine type and update tutorial steps

- Add enumerate_devices_by_engine() returning per-engine device lists
  without cross-engine dedup so frontend can filter correctly
- API /audio-devices now includes by_engine dict alongside flat list
- Frontend caches per-engine data, filters device dropdown by selected
  template's engine_type, refreshes on template change
- Reorder getting-started tutorial: add API docs and accent color steps
- Fix tutorial trigger button focus outline persisting on step 2
- Use accent color variable for tutorial pulse ring animation

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

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

@@ -10,9 +10,19 @@ router = APIRouter()
 
 @router.get("/api/v1/audio-devices", tags=["Audio"])
 async def list_audio_devices(_auth: AuthRequired):
-    """List available audio input/output devices for audio-reactive sources."""
+    """List available audio input/output devices for audio-reactive sources.
+
+    Returns a deduped flat list (backward compat) plus a ``by_engine`` dict
+    with per-engine device lists (no cross-engine dedup) so the frontend can
+    filter by the selected audio template's engine type.
+    """
     try:
         devices = AudioCaptureManager.enumerate_devices()
-        return {"devices": devices, "count": len(devices)}
+        by_engine = AudioCaptureManager.enumerate_devices_by_engine()
+        return {
+            "devices": devices,
+            "count": len(devices),
+            "by_engine": by_engine,
+        }
     except Exception as e:
-        return {"devices": [], "count": 0, "error": str(e)}
+        return {"devices": [], "count": 0, "by_engine": {}, "error": str(e)}