CSS: add GradientColorStripSource with visual editor

- Backend: GradientColorStripSource storage model, GradientColorStripStream
  with numpy interpolation (bidirectional stops, auto-size from device LED count),
  ColorStop Pydantic schema, API create/update/guard routes
- Frontend: gradient editor modal (canvas preview, draggable markers, stop rows),
  CSS hard-edge card swatch, locale keys (en + ru)
- Fixes: stop row mousedown no longer rebuilds DOM (buttons now clickable),
  position input max-width, bidir/remove button static width

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

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

@@ -26,7 +26,7 @@ from wled_controller.core.capture.calibration import (
 )
 from wled_controller.core.capture.screen_capture import get_available_displays
 from wled_controller.core.processing.processor_manager import ProcessorManager
-from wled_controller.storage.color_strip_source import PictureColorStripSource, StaticColorStripSource
+from wled_controller.storage.color_strip_source import GradientColorStripSource, PictureColorStripSource, StaticColorStripSource
 from wled_controller.storage.color_strip_store import ColorStripStore
 from wled_controller.storage.picture_source import ProcessedPictureSource, ScreenCapturePictureSource
 from wled_controller.storage.picture_source_store import PictureSourceStore
@@ -44,6 +44,16 @@ def _css_to_response(source, overlay_active: bool = False) -> ColorStripSourceRe
     if isinstance(source, PictureColorStripSource) and source.calibration:
         calibration = CalibrationSchema(**calibration_to_dict(source.calibration))
 
+    # Convert raw stop dicts to ColorStop schema objects for gradient sources
+    from wled_controller.api.schemas.color_strip_sources import ColorStop as ColorStopSchema
+    raw_stops = getattr(source, "stops", None)
+    stops = None
+    if raw_stops is not None:
+        try:
+            stops = [ColorStopSchema(**s) for s in raw_stops]
+        except Exception:
+            stops = None
+
     return ColorStripSourceResponse(
         id=source.id,
         name=source.name,
@@ -58,6 +68,7 @@ def _css_to_response(source, overlay_active: bool = False) -> ColorStripSourceRe
         led_count=getattr(source, "led_count", 0),
         calibration=calibration,
         color=getattr(source, "color", None),
+        stops=stops,
         description=source.description,
         overlay_active=overlay_active,
         created_at=source.created_at,
@@ -106,6 +117,8 @@ async def create_color_strip_source(
         if data.calibration is not None:
             calibration = calibration_from_dict(data.calibration.model_dump())
 
+        stops = [s.model_dump() for s in data.stops] if data.stops is not None else None
+
         source = store.create_source(
             name=data.name,
             source_type=data.source_type,
@@ -119,6 +132,7 @@ async def create_color_strip_source(
             led_count=data.led_count,
             calibration=calibration,
             color=data.color,
+            stops=stops,
             description=data.description,
         )
         return _css_to_response(source)
@@ -159,6 +173,8 @@ async def update_color_strip_source(
         if data.calibration is not None:
             calibration = calibration_from_dict(data.calibration.model_dump())
 
+        stops = [s.model_dump() for s in data.stops] if data.stops is not None else None
+
         source = store.update_source(
             source_id=source_id,
             name=data.name,
@@ -172,6 +188,7 @@ async def update_color_strip_source(
             led_count=data.led_count,
             calibration=calibration,
             color=data.color,
+            stops=stops,
             description=data.description,
         )
 
@@ -258,10 +275,10 @@ async def test_css_calibration(
         if body.edges:
             try:
                 source = store.get_source(source_id)
-                if isinstance(source, StaticColorStripSource):
+                if isinstance(source, (StaticColorStripSource, GradientColorStripSource)):
                     raise HTTPException(
                         status_code=400,
-                        detail="Calibration test is not applicable for static color strip sources",
+                        detail="Calibration test is not applicable for this color strip source type",
                     )
                 if isinstance(source, PictureColorStripSource) and source.calibration:
                     calibration = source.calibration
@@ -304,8 +321,8 @@ async def start_css_overlay(
     """Start screen overlay visualization for a color strip source."""
     try:
         source = store.get_source(source_id)
-        if isinstance(source, StaticColorStripSource):
-            raise HTTPException(status_code=400, detail="Overlay is not supported for static color strip sources")
+        if isinstance(source, (StaticColorStripSource, GradientColorStripSource)):
+            raise HTTPException(status_code=400, detail="Overlay is not supported for this color strip source type")
         if not isinstance(source, PictureColorStripSource):
             raise HTTPException(status_code=400, detail="Overlay only supported for picture color strip sources")
         if not source.calibration: