CSS: add led_count field; calibration dialog improvements; color corrections collapsible section

- Add explicit led_count to PictureColorStripSource (0 = auto from calibration)
- Stream pads with black or truncates to match led_count exactly
- Calibration dialog: show led_count input above visual editor in CSS mode
- Calibration dialog: pre-populate led_count with effective count (cal sum) when stored value is 0
- Calibration dialog: sync preview label live as led_count input changes
- CSS editor: group brightness/saturation/gamma into collapsible "Color Corrections" section

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

server/src/wled_controller/storage/color_strip_source.py

@@ -20,7 +20,6 @@ from wled_controller.core.capture.calibration import (
     CalibrationConfig,
     calibration_from_dict,
     calibration_to_dict,
-    create_default_calibration,
 )
 
 
@@ -53,6 +52,7 @@ class ColorStripSource:
             "smoothing": None,
             "interpolation_mode": None,
             "calibration": None,
+            "led_count": None,
         }
 
     @staticmethod
@@ -82,7 +82,7 @@ class ColorStripSource:
         calibration = (
             calibration_from_dict(calibration_data)
             if calibration_data
-            else create_default_calibration(0)
+            else CalibrationConfig(layout="clockwise", start_position="bottom_left")
         )
 
         # Only "picture" type for now; extend with elif branches for future types
@@ -97,6 +97,7 @@ class ColorStripSource:
             smoothing=data["smoothing"] if data.get("smoothing") is not None else 0.3,
             interpolation_mode=data.get("interpolation_mode") or "average",
             calibration=calibration,
+            led_count=data.get("led_count") or 0,
         )
 
 
@@ -115,7 +116,10 @@ class PictureColorStripSource(ColorStripSource):
     gamma: float = 1.0               # 1.0 = no correction; <1 = brighter, >1 = darker mids
     smoothing: float = 0.3           # temporal smoothing (0.0 = none, 1.0 = full)
     interpolation_mode: str = "average"   # "average" | "median" | "dominant"
-    calibration: CalibrationConfig = field(default_factory=lambda: create_default_calibration(0))
+    calibration: CalibrationConfig = field(
+        default_factory=lambda: CalibrationConfig(layout="clockwise", start_position="bottom_left")
+    )
+    led_count: int = 0               # explicit LED count; 0 = auto (derived from calibration)
 
     def to_dict(self) -> dict:
         d = super().to_dict()
@@ -127,4 +131,5 @@ class PictureColorStripSource(ColorStripSource):
         d["smoothing"] = self.smoothing
         d["interpolation_mode"] = self.interpolation_mode
         d["calibration"] = calibration_to_dict(self.calibration)
+        d["led_count"] = self.led_count
         return d

server/src/wled_controller/storage/color_strip_store.py

@@ -6,7 +6,7 @@ from datetime import datetime
 from pathlib import Path
 from typing import Dict, List, Optional
 
-from wled_controller.core.capture.calibration import calibration_to_dict
+from wled_controller.core.capture.calibration import CalibrationConfig, calibration_to_dict
 from wled_controller.storage.color_strip_source import (
     ColorStripSource,
     PictureColorStripSource,
@@ -98,6 +98,7 @@ class ColorStripStore:
         smoothing: float = 0.3,
         interpolation_mode: str = "average",
         calibration=None,
+        led_count: int = 0,
         description: Optional[str] = None,
     ) -> ColorStripSource:
         """Create a new color strip source.
@@ -105,8 +106,6 @@ class ColorStripStore:
         Raises:
             ValueError: If validation fails
         """
-        from wled_controller.core.capture.calibration import create_default_calibration
-
         if not name or not name.strip():
             raise ValueError("Name is required")
 
@@ -115,7 +114,7 @@ class ColorStripStore:
                 raise ValueError(f"Color strip source with name '{name}' already exists")
 
         if calibration is None:
-            calibration = create_default_calibration(0)
+            calibration = CalibrationConfig(layout="clockwise", start_position="bottom_left")
 
         source_id = f"css_{uuid.uuid4().hex[:8]}"
         now = datetime.utcnow()
@@ -135,6 +134,7 @@ class ColorStripStore:
             smoothing=smoothing,
             interpolation_mode=interpolation_mode,
             calibration=calibration,
+            led_count=led_count,
         )
 
         self._sources[source_id] = source
@@ -155,6 +155,7 @@ class ColorStripStore:
         smoothing: Optional[float] = None,
         interpolation_mode: Optional[str] = None,
         calibration=None,
+        led_count: Optional[int] = None,
         description: Optional[str] = None,
     ) -> ColorStripSource:
         """Update an existing color strip source.
@@ -193,6 +194,8 @@ class ColorStripStore:
                 source.interpolation_mode = interpolation_mode
             if calibration is not None:
                 source.calibration = calibration
+            if led_count is not None:
+                source.led_count = led_count
 
         source.updated_at = datetime.utcnow()
         self._save()