Add collapsible card sections with name filtering

Introduces CardSection class that wraps each card grid with a collapsible
header and inline filter input. Collapse state persists in localStorage,
filter value survives auto-refresh re-renders. When filter is active the
add-card button is hidden. Applied to all 13 sections across Targets,
Sources, and Profiles tabs.

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

server/src/wled_controller/static/css/streams.css

@@ -603,6 +603,61 @@
     border-bottom: 1px solid var(--border-color);
 }
 
+/* ── Collapsible card sections (cs-*) ── */
+
+.cs-header {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    cursor: pointer;
+    user-select: none;
+}
+
+.cs-chevron {
+    font-size: 0.65rem;
+    color: var(--text-secondary);
+    width: 12px;
+    display: inline-block;
+    flex-shrink: 0;
+}
+
+.cs-title {
+    flex-shrink: 0;
+}
+
+.cs-count {
+    background: var(--border-color);
+    color: var(--text-secondary);
+    border-radius: 10px;
+    padding: 0 7px;
+    font-size: 0.75rem;
+    font-weight: 600;
+    flex-shrink: 0;
+}
+
+.cs-filter {
+    margin-left: auto;
+    width: 160px;
+    max-width: 40%;
+    padding: 3px 8px !important;
+    font-size: 0.78rem !important;
+    border: 1px solid var(--border-color) !important;
+    border-radius: 12px !important;
+    background: var(--bg-color) !important;
+    color: var(--text-color) !important;
+    outline: none;
+    box-shadow: none !important;
+}
+
+.cs-filter:focus {
+    border-color: var(--primary-color) !important;
+}
+
+.cs-filter::placeholder {
+    color: var(--text-secondary);
+    font-size: 0.75rem;
+}
+
 /* Responsive adjustments */
 @media (max-width: 768px) {
     .templates-grid {