feat: expand color strip sources with gradient references and effect improvements

Add gradient_id field to color strip sources for referencing reusable
gradient entities. Improve audio stream processing and effect stream
with new parameters.

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

@@ -567,6 +567,13 @@ async def preview_color_strip_ws(
         if not stream_cls:
             raise ValueError(f"Unsupported preview source_type: {source.source_type}")
         s = stream_cls(source)
+        # Inject gradient store for palette resolution
+        if hasattr(s, "set_gradient_store"):
+            try:
+                from wled_controller.api.dependencies import get_gradient_store
+                s.set_gradient_store(get_gradient_store())
+            except Exception:
+                pass
         if hasattr(s, "configure"):
             s.configure(led_count)
         # Inject sync clock if requested

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

@@ -70,6 +70,8 @@ class ColorStripSourceCreate(BaseModel):
     scale: Optional[float] = Field(None, description="Spatial scale 0.5-5.0", ge=0.5, le=5.0)
     mirror: Optional[bool] = Field(None, description="Mirror/bounce mode (meteor/comet)")
     custom_palette: Optional[List[List[float]]] = Field(None, description="Custom palette stops [[pos,R,G,B],...]")
+    # gradient entity reference (effect, gradient, audio types)
+    gradient_id: Optional[str] = Field(None, description="Gradient entity ID (overrides palette/inline stops)")
     # gradient-type easing
     easing: Optional[str] = Field(None, description="Gradient interpolation easing: linear|ease_in_out|step|cubic")
     # composite-type fields
@@ -135,6 +137,8 @@ class ColorStripSourceUpdate(BaseModel):
     scale: Optional[float] = Field(None, description="Spatial scale 0.5-5.0", ge=0.5, le=5.0)
     mirror: Optional[bool] = Field(None, description="Mirror/bounce mode")
     custom_palette: Optional[List[List[float]]] = Field(None, description="Custom palette stops [[pos,R,G,B],...]")
+    # gradient entity reference (effect, gradient, audio types)
+    gradient_id: Optional[str] = Field(None, description="Gradient entity ID (overrides palette/inline stops)")
     # gradient-type easing
     easing: Optional[str] = Field(None, description="Gradient interpolation easing: linear|ease_in_out|step|cubic")
     # composite-type fields
@@ -202,6 +206,7 @@ class ColorStripSourceResponse(BaseModel):
     scale: Optional[float] = Field(None, description="Spatial scale")
     mirror: Optional[bool] = Field(None, description="Mirror/bounce mode")
     custom_palette: Optional[List[List[float]]] = Field(None, description="Custom palette stops")
+    gradient_id: Optional[str] = Field(None, description="Gradient entity ID")
     # gradient-type easing
     easing: Optional[str] = Field(None, description="Gradient interpolation easing")
     # composite-type fields