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/pattern-templates.js

@@ -13,6 +13,7 @@ import {
     patternEditorHoverHit, setPatternEditorHoverHit,
     PATTERN_RECT_COLORS,
     PATTERN_RECT_BORDERS,
+    streamsCache,
 } from '../core/state.js';
 import { API_BASE, getHeaders, fetchWithAuth, escapeHtml } from '../core/api.js';
 import { t } from '../core/i18n.js';
@@ -76,8 +77,7 @@ export function createPatternTemplateCard(pt) {
 export async function showPatternTemplateEditor(templateId = null, cloneData = null) {
     try {
         // Load sources for background capture
-        const sourcesResp = await fetchWithAuth('/picture-sources').catch(() => null);
-        const sources = (sourcesResp && sourcesResp.ok) ? (await sourcesResp.json()).streams || [] : [];
+        const sources = await streamsCache.fetch().catch(() => []);
 
         const bgSelect = document.getElementById('pattern-bg-source');
         bgSelect.innerHTML = '';