Remove per-source speed, fix device dirty check, and add frontend caching

Speed is now exclusively controlled via sync clocks — CSS sources no longer
carry their own speed/cycle_speed fields. Streams default to 1.0× when no
clock is assigned. Also fixes false-positive dirty check on the device
settings modal (array reference comparison) and converts several frontend
modules to use DataCache for consistent API response caching.

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

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

@@ -8,7 +8,7 @@ import {
     _kcNameManuallyEdited, set_kcNameManuallyEdited,
     kcWebSockets,
     PATTERN_RECT_BORDERS,
-    _cachedValueSources, valueSourcesCache,
+    _cachedValueSources, valueSourcesCache, streamsCache,
 } from '../core/state.js';
 import { API_BASE, getHeaders, fetchWithAuth, escapeHtml } from '../core/api.js';
 import { t } from '../core/i18n.js';
@@ -413,12 +413,11 @@ function _populateKCBrightnessVsDropdown(selectedId = '') {
 export async function showKCEditor(targetId = null, cloneData = null) {
     try {
         // Load sources, pattern templates, and value sources in parallel
-        const [sourcesResp, patResp, valueSources] = await Promise.all([
-            fetchWithAuth('/picture-sources').catch(() => null),
+        const [sources, patResp, valueSources] = await Promise.all([
+            streamsCache.fetch().catch(() => []),
             fetchWithAuth('/pattern-templates').catch(() => null),
             valueSourcesCache.fetch(),
         ]);
-        const sources = (sourcesResp && sourcesResp.ok) ? (await sourcesResp.json()).streams || [] : [];
         const patTemplates = (patResp && patResp.ok) ? (await patResp.json()).templates || [] : [];
 
         // Populate source select