Add multi-segment LED targets, replace single color strip source + skip fields

Each target now has a segments list where each segment maps a color strip
source to a pixel range (start/end) on the device with optional reverse.
This enables composing multiple visualizations on a single LED strip.
Old targets auto-migrate from the single source format on load.

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

server/src/wled_controller/static/js/app.js

@@ -82,6 +82,7 @@ import {
 import {
     loadTargetsTab, loadTargets, switchTargetSubTab,
     showTargetEditor, closeTargetEditorModal, forceCloseTargetEditorModal, saveTargetEditor,
+    addTargetSegment, removeTargetSegment,
     startTargetProcessing, stopTargetProcessing,
     startTargetOverlay, stopTargetOverlay, deleteTarget,
 } from './features/targets.js';
@@ -265,6 +266,8 @@ Object.assign(window, {
     closeTargetEditorModal,
     forceCloseTargetEditorModal,
     saveTargetEditor,
+    addTargetSegment,
+    removeTargetSegment,
     startTargetProcessing,
     stopTargetProcessing,
     startTargetOverlay,