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/core/audio/audio_capture.py

@@ -292,3 +292,31 @@ class AudioCaptureManager:
             except Exception as e:
                 logger.error(f"Error enumerating devices for engine '{engine_type}': {e}")
         return result
+
+    @staticmethod
+    def enumerate_devices_by_engine() -> Dict[str, List[dict]]:
+        """List available audio devices grouped by engine type.
+
+        Unlike enumerate_devices(), does NOT deduplicate across engines.
+        Each engine's devices are returned with their engine-specific indices.
+        """
+        result: Dict[str, List[dict]] = {}
+        for engine_type, engine_class in AudioEngineRegistry.get_all_engines().items():
+            try:
+                if not engine_class.is_available():
+                    continue
+                devices = []
+                for dev in engine_class.enumerate_devices():
+                    devices.append({
+                        "index": dev.index,
+                        "name": dev.name,
+                        "is_input": dev.is_input,
+                        "is_loopback": dev.is_loopback,
+                        "channels": dev.channels,
+                        "default_samplerate": dev.default_samplerate,
+                        "engine_type": engine_type,
+                    })
+                result[engine_type] = devices
+            except Exception as e:
+                logger.error(f"Error enumerating devices for engine '{engine_type}': {e}")
+        return result