Add brightness control to Key Colors targets with HAOS integration

Adds brightness (0.0-1.0) to KeyColorsSettings, applies scaling in the
KC processing pipeline after smoothing, exposes a slider on the WebUI
target card, and creates a HA number entity for KC target brightness.

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

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

@@ -34,7 +34,7 @@ KC_WORK_SIZE = (160, 90)  # (width, height) — small enough for fast color calc
 # CPU-bound frame processing (runs in thread pool via asyncio.to_thread)
 # ---------------------------------------------------------------------------
 
-def _process_kc_frame(capture, rect_names, rect_bounds, calc_fn, prev_colors_arr, smoothing):
+def _process_kc_frame(capture, rect_names, rect_bounds, calc_fn, prev_colors_arr, smoothing, brightness):
     """All CPU-bound work for one KC frame.
 
     Returns (colors, colors_arr, timing_ms) where:
@@ -59,7 +59,13 @@ def _process_kc_frame(capture, rect_names, rect_bounds, calc_fn, prev_colors_arr
     if prev_colors_arr is not None and smoothing > 0:
         colors_arr = colors_arr * (1 - smoothing) + prev_colors_arr * smoothing
 
-    colors_u8 = np.clip(colors_arr, 0, 255).astype(np.uint8)
+    # Apply brightness scaling
+    if brightness < 1.0:
+        output_arr = colors_arr * brightness
+    else:
+        output_arr = colors_arr
+
+    colors_u8 = np.clip(output_arr, 0, 255).astype(np.uint8)
     t2 = time.perf_counter()
 
     # Build output dict
@@ -256,6 +262,7 @@ class KCTargetProcessor(TargetProcessor):
 
         target_fps = settings.fps
         smoothing = settings.smoothing
+        brightness = settings.brightness
 
         # Select color calculation function
         calc_fns = {
@@ -328,7 +335,7 @@ class KCTargetProcessor(TargetProcessor):
                     colors, colors_arr, frame_timing = await asyncio.to_thread(
                         _process_kc_frame,
                         capture, rect_names, rect_bounds, calc_fn,
-                        prev_colors_arr, smoothing,
+                        prev_colors_arr, smoothing, brightness,
                     )
 
                     prev_colors_arr = colors_arr