Rework API input CSS: segments, remove led_count, HAOS light, test preview

API Input CSS rework:
- Remove led_count field from ApiInputColorStripSource (always auto-sizes)
- Add segment-based payload: solid, per_pixel, gradient modes
- Segments applied in order (last wins on overlap), auto-grow buffer
- Backward compatible: legacy {"colors": [...]} still works
- Pydantic validation: mode-specific field requirements

Test preview:
- Enable test preview button on api_input cards
- Hide LED/FPS controls for api_input (sender controls those)
- Show input source selector for all CSS tests (preselected)
- FPS sparkline chart using shared createFpsSparkline (same as target cards)
- Server only sends frames when push_generation changes (no idle frames)

HAOS integration:
- New light.py: ApiInputLight entity per api_input source (RGB + brightness)
- turn_on pushes solid segment, turn_off pushes fallback color
- Register wled_screen_controller.set_leds service for arbitrary segments
- New services.yaml with field definitions
- Coordinator: push_colors() and push_segments() methods
- Platform.LIGHT added to platforms list

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -3,7 +3,7 @@
 from datetime import datetime
 from typing import Dict, List, Literal, Optional
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, model_validator
 
 from wled_controller.api.schemas.devices import Calibration
 
@@ -237,10 +237,52 @@ class ColorStripSourceListResponse(BaseModel):
     count: int = Field(description="Number of sources")
 
 
-class ColorPushRequest(BaseModel):
-    """Request to push raw LED colors to an api_input source."""
+class SegmentPayload(BaseModel):
+    """A single segment for segment-based LED color updates."""
 
-    colors: List[List[int]] = Field(description="LED color array [[R,G,B], ...] (0-255 each)")
+    start: int = Field(ge=0, description="Starting LED index")
+    length: int = Field(ge=1, description="Number of LEDs in segment")
+    mode: Literal["solid", "per_pixel", "gradient"] = Field(description="Fill mode")
+    color: Optional[List[int]] = Field(None, description="RGB for solid mode [R,G,B]")
+    colors: Optional[List[List[int]]] = Field(None, description="Colors for per_pixel/gradient [[R,G,B],...]")
+
+    @model_validator(mode="after")
+    def _validate_mode_fields(self) -> "SegmentPayload":
+        if self.mode == "solid":
+            if self.color is None or len(self.color) != 3:
+                raise ValueError("solid mode requires 'color' as a list of 3 ints [R,G,B]")
+            if not all(0 <= c <= 255 for c in self.color):
+                raise ValueError("solid color values must be 0-255")
+        elif self.mode == "per_pixel":
+            if not self.colors:
+                raise ValueError("per_pixel mode requires non-empty 'colors' list")
+            for c in self.colors:
+                if len(c) != 3:
+                    raise ValueError("each color in per_pixel must be [R,G,B]")
+        elif self.mode == "gradient":
+            if not self.colors or len(self.colors) < 2:
+                raise ValueError("gradient mode requires 'colors' with at least 2 stops")
+            for c in self.colors:
+                if len(c) != 3:
+                    raise ValueError("each color stop in gradient must be [R,G,B]")
+        return self
+
+
+class ColorPushRequest(BaseModel):
+    """Request to push raw LED colors to an api_input source.
+
+    Accepts either 'colors' (legacy flat array) or 'segments' (new segment-based).
+    At least one must be provided.
+    """
+
+    colors: Optional[List[List[int]]] = Field(None, description="LED color array [[R,G,B], ...] (0-255 each)")
+    segments: Optional[List[SegmentPayload]] = Field(None, description="Segment-based color updates")
+
+    @model_validator(mode="after")
+    def _require_colors_or_segments(self) -> "ColorPushRequest":
+        if self.colors is None and self.segments is None:
+            raise ValueError("Either 'colors' or 'segments' must be provided")
+        return self
 
 
 class NotifyRequest(BaseModel):