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/static/js/app.js

@@ -58,6 +58,7 @@ import {
     createKCTargetCard, testKCTarget, toggleKCTestAutoRefresh,
     showKCEditor, closeKCEditorModal, forceCloseKCEditorModal, saveKCEditor,
     deleteKCTarget, disconnectAllKCWebSockets,
+    updateKCBrightnessLabel, saveKCBrightness,
 } from './features/kc-targets.js';
 import {
     createPatternTemplateCard,
@@ -210,6 +211,8 @@ Object.assign(window, {
     saveKCEditor,
     deleteKCTarget,
     disconnectAllKCWebSockets,
+    updateKCBrightnessLabel,
+    saveKCBrightness,
 
     // pattern-templates
     createPatternTemplateCard,