feat: add music sync viz modes and auto_gain audio filter

Add 4 new audio visualization modes powered by MusicAnalyzer:
- pulse_on_beat: BPM-synced pulsing with smooth beat phase
- energy_gradient: bass/mid/treble mapped to scrolling gradient
- spectrum_bands: three VU zones for frequency bands
- strobe_on_drop: state-driven strobe on detected musical drops

MusicAnalyzer provides BPM estimation (median IBI), beat phase tracking,
asymmetric energy envelope, 3-band frequency splitting, and drop
detection state machine (idle/buildup/drop/recovery).

Add auto_gain audio filter for automatic level normalization via rolling
peak tracking with configurable target level and response time.

Deprecate auto_gain on Audio Value Source (use the filter instead).

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

@@ -191,6 +191,7 @@ _RESPONSE_MAP: dict = {
         color=s.color.to_dict(),
         color_peak=s.color_peak.to_dict(),
         mirror=s.mirror,
+        beat_decay=s.beat_decay.to_dict(),
     ),
     ApiInputColorStripSource: lambda s, kw: ApiInputCSSResponse(
         **kw,

server/src/wled_controller/api/schemas/color_strip_sources.py

@@ -164,6 +164,7 @@ class AudioCSSResponse(_CSSResponseBase):
     color: Any = Field(description="Primary color")
     color_peak: Any = Field(description="Peak color")
     mirror: bool = Field(description="Mirror mode")
+    beat_decay: Any = Field(default=0.15, description="Beat pulse decay rate (music modes)")
 
 
 class ApiInputCSSResponse(_CSSResponseBase):
@@ -340,6 +341,9 @@ class AudioCSSCreate(_CSSCreateBase):
     color: Any = Field(default=None, description="Primary color")
     color_peak: Any = Field(default=None, description="Peak color [R,G,B]")
     mirror: Optional[bool] = Field(None, description="Mirror mode")
+    beat_decay: Any = Field(
+        default=None, description="Beat pulse decay rate (music modes, 0.01-0.5)"
+    )
 
 
 class ApiInputCSSCreate(_CSSCreateBase):
@@ -527,6 +531,7 @@ class AudioCSSUpdate(_CSSUpdateBase):
     color: Any = Field(default=None, description="Primary color")
     color_peak: Any = Field(default=None, description="Peak color [R,G,B]")
     mirror: Optional[bool] = Field(None, description="Mirror mode")
+    beat_decay: Any = Field(default=None, description="Beat pulse decay rate (music modes)")
 
 
 class ApiInputCSSUpdate(_CSSUpdateBase):