Fix gamma correction, frame interpolation flicker, and target card redraws

- Fix inverted gamma formula: use (i/255)^gamma instead of (i/255)^(1/gamma)
  so gamma>1 correctly darkens midtones (standard LED gamma correction)
- Fix frame interpolation flicker: move interp buffer update after temporal
  smoothing so idle-tick output is consistent with new-frame output
- Fix target card hover/animation reset: use stable placeholder values in
  card HTML for volatile metrics (data-tm attributes), patch real values
  in-place after reconcile instead of replacing entire card DOM element

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

server/src/wled_controller/core/filters/gamma.py

@@ -20,7 +20,7 @@ class GammaFilter(PostprocessingFilter):
         super().__init__(options)
         value = self.options["value"]
         lut = np.arange(256, dtype=np.float32) / 255.0
-        np.power(lut, 1.0 / value, out=lut)
+        np.power(lut, value, out=lut)
         self._lut = np.clip(lut * 255.0, 0, 255).astype(np.uint8)
 
     @classmethod

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

@@ -64,13 +64,13 @@ def _build_gamma_lut(gamma: float) -> np.ndarray:
     """Build a 256-entry uint8 LUT for gamma correction.
 
     gamma=1.0: identity (no correction)
-    gamma<1.0: brighter midtones
-    gamma>1.0: darker midtones
+    gamma<1.0: brighter midtones (gamma < 1 lifts shadows)
+    gamma>1.0: darker midtones  (standard LED gamma, e.g. 2.2–2.8)
     """
     if gamma == 1.0:
         return np.arange(256, dtype=np.uint8)
     lut = np.array(
-        [min(255, int(((i / 255.0) ** (1.0 / gamma)) * 255 + 0.5)) for i in range(256)],
+        [min(255, int(((i / 255.0) ** gamma) * 255 + 0.5)) for i in range(256)],
         dtype=np.uint8,
     )
     return lut
@@ -407,13 +407,6 @@ class PictureColorStripStream(ColorStripStream):
                             frame_buf[:] = led_colors
                         led_colors = frame_buf
 
-                    # Update interpolation buffers (raw colors, before corrections)
-                    if self._frame_interpolation:
-                        self._interp_from = self._interp_to
-                        self._interp_to = led_colors.copy()
-                        self._interp_start = loop_start
-                        self._interp_duration = max(interval, 0.001)
-
                     # Temporal smoothing (pre-allocated uint16 scratch)
                     smoothing = self._smoothing
                     if (
@@ -426,6 +419,15 @@ class PictureColorStripStream(ColorStripStream):
                                    int(smoothing * 256), led_colors)
                     t3 = time.perf_counter()
 
+                    # Update interpolation buffers (smoothed colors, before corrections)
+                    # Must be AFTER smoothing so idle-tick interpolation produces
+                    # output consistent with new-frame ticks (both smoothed).
+                    if self._frame_interpolation:
+                        self._interp_from = self._interp_to
+                        self._interp_to = led_colors.copy()
+                        self._interp_start = loop_start
+                        self._interp_duration = max(interval, 0.001)
+
                     # Saturation (pre-allocated int32 scratch)
                     saturation = self._saturation
                     if saturation != 1.0: