Remove target segments, use single color strip source per target

Segments are redundant now that the "mapped" CSS type handles spatial
multiplexing internally. Each target now references one color_strip_source_id
instead of an array of segments with start/end/reverse ranges.

Backward compat: existing targets with old segments format are migrated
on load by extracting the first segment's CSS source ID.

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

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

@@ -85,7 +85,6 @@ import {
 import {
     loadTargetsTab, loadTargets, switchTargetSubTab,
     showTargetEditor, closeTargetEditorModal, forceCloseTargetEditorModal, saveTargetEditor,
-    addTargetSegment, removeTargetSegment, syncSegmentsMappedMode,
     startTargetProcessing, stopTargetProcessing,
     startTargetOverlay, stopTargetOverlay, deleteTarget,
     cloneTarget,
@@ -283,9 +282,6 @@ Object.assign(window, {
     closeTargetEditorModal,
     forceCloseTargetEditorModal,
     saveTargetEditor,
-    addTargetSegment,
-    removeTargetSegment,
-    syncSegmentsMappedMode,
     startTargetProcessing,
     stopTargetProcessing,
     startTargetOverlay,