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/storage/color_strip_source.py

@@ -7,9 +7,7 @@ calibration, color correction, smoothing, and FPS.
 Current types:
   PictureColorStripSource  —  derives LED colors from a PictureSource (screen capture)
   StaticColorStripSource   —  constant solid color fills all LEDs
-
-Future types (not yet implemented):
-  GradientColorStripSource —  animated gradient
+  GradientColorStripSource —  linear gradient across all LEDs from user-defined color stops
 """
 
 from dataclasses import dataclass, field
@@ -54,6 +52,7 @@ class ColorStripSource:
             "calibration": None,
             "led_count": None,
             "color": None,
+            "stops": None,
         }
 
     @staticmethod
@@ -99,6 +98,16 @@ class ColorStripSource:
                 led_count=data.get("led_count") or 0,
             )
 
+        if source_type == "gradient":
+            raw_stops = data.get("stops")
+            stops = raw_stops if isinstance(raw_stops, list) else []
+            return GradientColorStripSource(
+                id=sid, name=name, source_type="gradient",
+                created_at=created_at, updated_at=updated_at, description=description,
+                stops=stops,
+                led_count=data.get("led_count") or 0,
+            )
+
         # Default: "picture" type
         return PictureColorStripSource(
             id=sid, name=name, source_type=source_type,
@@ -166,3 +175,28 @@ class StaticColorStripSource(ColorStripSource):
         d["color"] = list(self.color)
         d["led_count"] = self.led_count
         return d
+
+
+@dataclass
+class GradientColorStripSource(ColorStripSource):
+    """Color strip source that produces a linear gradient across all LEDs.
+
+    The gradient is defined by color stops at relative positions (0.0–1.0).
+    Each stop has a primary color; optionally a second "right" color to create
+    a hard discontinuity (bidirectional stop) at that position.
+
+    LED count auto-sizes from the connected device when led_count == 0.
+    """
+
+    # Each stop: {"position": float, "color": [R,G,B], "color_right": [R,G,B] | null}
+    stops: list = field(default_factory=lambda: [
+        {"position": 0.0, "color": [255, 0, 0]},
+        {"position": 1.0, "color": [0, 0, 255]},
+    ])
+    led_count: int = 0  # 0 = use device LED count
+
+    def to_dict(self) -> dict:
+        d = super().to_dict()
+        d["stops"] = [dict(s) for s in self.stops]
+        d["led_count"] = self.led_count
+        return d

server/src/wled_controller/storage/color_strip_store.py

@@ -9,6 +9,7 @@ from typing import Dict, List, Optional
 from wled_controller.core.capture.calibration import CalibrationConfig, calibration_to_dict
 from wled_controller.storage.color_strip_source import (
     ColorStripSource,
+    GradientColorStripSource,
     PictureColorStripSource,
     StaticColorStripSource,
 )
@@ -101,6 +102,7 @@ class ColorStripStore:
         calibration=None,
         led_count: int = 0,
         color: Optional[list] = None,
+        stops: Optional[list] = None,
         description: Optional[str] = None,
     ) -> ColorStripSource:
         """Create a new color strip source.
@@ -130,6 +132,20 @@ class ColorStripStore:
                 color=rgb,
                 led_count=led_count,
             )
+        elif source_type == "gradient":
+            source = GradientColorStripSource(
+                id=source_id,
+                name=name,
+                source_type="gradient",
+                created_at=now,
+                updated_at=now,
+                description=description,
+                stops=stops if isinstance(stops, list) else [
+                    {"position": 0.0, "color": [255, 0, 0]},
+                    {"position": 1.0, "color": [0, 0, 255]},
+                ],
+                led_count=led_count,
+            )
         else:
             if calibration is None:
                 calibration = CalibrationConfig(layout="clockwise", start_position="bottom_left")
@@ -171,6 +187,7 @@ class ColorStripStore:
         calibration=None,
         led_count: Optional[int] = None,
         color: Optional[list] = None,
+        stops: Optional[list] = None,
         description: Optional[str] = None,
     ) -> ColorStripSource:
         """Update an existing color strip source.
@@ -217,6 +234,11 @@ class ColorStripStore:
                     source.color = color
             if led_count is not None:
                 source.led_count = led_count
+        elif isinstance(source, GradientColorStripSource):
+            if stops is not None and isinstance(stops, list):
+                source.stops = stops
+            if led_count is not None:
+                source.led_count = led_count
 
         source.updated_at = datetime.utcnow()
         self._save()