Add reusable DataCache class, unify frontend cache patterns

- Create DataCache class with fetch deduplication, invalidation, subscribers
- Instantiate 10 cache instances in state.js (streams, templates, sources, etc.)
- Replace inline fetch+parse+set patterns with cache.fetch() calls across modules
- Eliminate dual _scenesCache/_presetsCache sync via shared scenePresetsCache
- Remove 9 now-unused setter functions from state.js
- Clean up unused setter imports from audio-sources, value-sources, displays

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

server/src/wled_controller/static/js/features/targets.js

@@ -8,7 +8,7 @@ import {
     _deviceBrightnessCache,
     kcWebSockets,
     ledPreviewWebSockets,
-    _cachedValueSources, set_cachedValueSources,
+    _cachedValueSources, valueSourcesCache,
 } from '../core/state.js';
 import { API_BASE, getHeaders, fetchWithAuth, escapeHtml } from '../core/api.js';
 import { t } from '../core/i18n.js';
@@ -241,18 +241,14 @@ function _populateBrightnessVsDropdown(selectedId = '') {
 export async function showTargetEditor(targetId = null, cloneData = null) {
     try {
         // Load devices, CSS sources, and value sources for dropdowns
-        const [devicesResp, cssResp, vsResp] = await Promise.all([
+        const [devicesResp, cssResp] = await Promise.all([
             fetch(`${API_BASE}/devices`, { headers: getHeaders() }),
             fetchWithAuth('/color-strip-sources'),
-            fetchWithAuth('/value-sources'),
+            valueSourcesCache.fetch(),
         ]);
 
         const devices = devicesResp.ok ? (await devicesResp.json()).devices || [] : [];
         const cssSources = cssResp.ok ? (await cssResp.json()).sources || [] : [];
-        if (vsResp.ok) {
-            const vsData = await vsResp.json();
-            set_cachedValueSources(vsData.sources || []);
-        }
         set_targetEditorDevices(devices);
         _editorCssSources = cssSources;
 
@@ -478,13 +474,13 @@ export async function loadTargetsTab() {
 
     try {
         // Fetch devices, targets, CSS sources, picture sources, pattern templates, and value sources in parallel
-        const [devicesResp, targetsResp, cssResp, psResp, patResp, vsResp, asResp] = await Promise.all([
+        const [devicesResp, targetsResp, cssResp, psResp, patResp, valueSrcArr, asResp] = await Promise.all([
             fetchWithAuth('/devices'),
             fetchWithAuth('/picture-targets'),
             fetchWithAuth('/color-strip-sources').catch(() => null),
             fetchWithAuth('/picture-sources').catch(() => null),
             fetchWithAuth('/pattern-templates').catch(() => null),
-            fetchWithAuth('/value-sources').catch(() => null),
+            valueSourcesCache.fetch().catch(() => []),
             fetchWithAuth('/audio-sources').catch(() => null),
         ]);
 
@@ -515,10 +511,7 @@ export async function loadTargetsTab() {
         }
 
         let valueSourceMap = {};
-        if (vsResp && vsResp.ok) {
-            const vsData = await vsResp.json();
-            (vsData.sources || []).forEach(s => { valueSourceMap[s.id] = s; });
-        }
+        valueSrcArr.forEach(s => { valueSourceMap[s.id] = s; });
 
         let audioSourceMap = {};
         if (asResp && asResp.ok) {