Add audio capture engine template system with multi-backend support

Introduces an engine+template abstraction for audio capture, mirroring the
existing screen capture engine pattern. This enables multiple audio backends
(WASAPI for Windows, sounddevice for cross-platform) with per-source
engine configuration via reusable templates.

Backend:
- AudioCaptureEngine ABC with WasapiEngine and SounddeviceEngine implementations
- AudioEngineRegistry for engine discovery and factory creation
- AudioAnalyzer class decouples FFT/RMS/beat analysis from engine-specific capture
- ManagedAudioStream wraps engine stream + analyzer in background thread
- AudioCaptureTemplate model and AudioTemplateStore with JSON CRUD
- AudioCaptureManager keyed by (engine_type, device_index, is_loopback)
- Auto-migration: default template created on startup, assigned to existing sources
- Full REST API: CRUD for audio templates + engine listing with availability flags
- audio_template_id added to MultichannelAudioSource model and API schemas

Frontend:
- Audio template cards in Streams > Audio tab with engine badge and config details
- Audio template editor modal with engine selector and dynamic config fields
- Audio template dropdown in multichannel audio source editor
- Template name crosslink badge on multichannel audio source cards
- Confirm modal z-index fix (always stacks above editor modals)
- i18n keys for EN and RU

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

server/src/wled_controller/api/dependencies.py

@@ -9,6 +9,7 @@ from wled_controller.storage.picture_source_store import PictureSourceStore
 from wled_controller.storage.picture_target_store import PictureTargetStore
 from wled_controller.storage.color_strip_store import ColorStripStore
 from wled_controller.storage.audio_source_store import AudioSourceStore
+from wled_controller.storage.audio_template_store import AudioTemplateStore
 from wled_controller.storage.value_source_store import ValueSourceStore
 from wled_controller.storage.profile_store import ProfileStore
 from wled_controller.core.profiles.profile_engine import ProfileEngine
@@ -22,6 +23,7 @@ _picture_source_store: PictureSourceStore | None = None
 _picture_target_store: PictureTargetStore | None = None
 _color_strip_store: ColorStripStore | None = None
 _audio_source_store: AudioSourceStore | None = None
+_audio_template_store: AudioTemplateStore | None = None
 _value_source_store: ValueSourceStore | None = None
 _processor_manager: ProcessorManager | None = None
 _profile_store: ProfileStore | None = None
@@ -84,6 +86,13 @@ def get_audio_source_store() -> AudioSourceStore:
     return _audio_source_store
 
 
+def get_audio_template_store() -> AudioTemplateStore:
+    """Get audio template store dependency."""
+    if _audio_template_store is None:
+        raise RuntimeError("Audio template store not initialized")
+    return _audio_template_store
+
+
 def get_value_source_store() -> ValueSourceStore:
     """Get value source store dependency."""
     if _value_source_store is None:
@@ -122,6 +131,7 @@ def init_dependencies(
     picture_target_store: PictureTargetStore | None = None,
     color_strip_store: ColorStripStore | None = None,
     audio_source_store: AudioSourceStore | None = None,
+    audio_template_store: AudioTemplateStore | None = None,
     value_source_store: ValueSourceStore | None = None,
     profile_store: ProfileStore | None = None,
     profile_engine: ProfileEngine | None = None,
@@ -129,7 +139,8 @@ def init_dependencies(
     """Initialize global dependencies."""
     global _device_store, _template_store, _processor_manager
     global _pp_template_store, _pattern_template_store, _picture_source_store, _picture_target_store
-    global _color_strip_store, _audio_source_store, _value_source_store, _profile_store, _profile_engine
+    global _color_strip_store, _audio_source_store, _audio_template_store
+    global _value_source_store, _profile_store, _profile_engine
     _device_store = device_store
     _template_store = template_store
     _processor_manager = processor_manager
@@ -139,6 +150,7 @@ def init_dependencies(
     _picture_target_store = picture_target_store
     _color_strip_store = color_strip_store
     _audio_source_store = audio_source_store
+    _audio_template_store = audio_template_store
     _value_source_store = value_source_store
     _profile_store = profile_store
     _profile_engine = profile_engine