Add value source card crosslinks and fix scene initial value bias

- Audio value source cards link to the referenced audio source
- Adaptive scene cards link to the referenced picture source
- Fix SceneValueStream starting at 0.5 regardless of actual scene;
  first frame now skips smoothing to avoid artificial bias
- Add crosslinks guidance to CLAUDE.md card appearance section

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

server/src/wled_controller/core/processing/value_stream.py

@@ -449,7 +449,7 @@ class SceneValueStream(ValueStream):
         self._max = max_value
         self._live_stream_manager = live_stream_manager
         self._live_stream = None
-        self._prev_value = 0.5  # neutral start
+        self._prev_value = None  # None = no frame seen yet; skip smoothing on first frame
 
     def start(self) -> None:
         if self._live_stream_manager and self._picture_source_id:
@@ -471,15 +471,15 @@ class SceneValueStream(ValueStream):
             except Exception as e:
                 logger.warning(f"SceneValueStream failed to release live stream: {e}")
             self._live_stream = None
-        self._prev_value = 0.5
+        self._prev_value = None
 
     def get_value(self) -> float:
         if self._live_stream is None:
-            return self._prev_value
+            return self._prev_value if self._prev_value is not None else 0.0
 
         frame = self._live_stream.get_latest_frame()
         if frame is None:
-            return self._prev_value
+            return self._prev_value if self._prev_value is not None else 0.0
 
         # Fast luminance: subsample to ~64x64 via numpy stride (zero-copy view)
         img = frame.image
@@ -500,8 +500,11 @@ class SceneValueStream(ValueStream):
         if self._behavior == "complement":
             raw = 1.0 - raw
 
-        # Temporal smoothing (EMA)
-        smoothed = self._smoothing * self._prev_value + (1.0 - self._smoothing) * raw
+        # Temporal smoothing (EMA) — skip on first frame (no history to blend with)
+        if self._prev_value is None:
+            smoothed = raw
+        else:
+            smoothed = self._smoothing * self._prev_value + (1.0 - self._smoothing) * raw
         self._prev_value = smoothed
 
         # Map to output range