Add power toggle button to LED device cards

WLED: native on/off via JSON API. Adalight: sends all-black frame
to blank LEDs (uses existing client if target is running, otherwise
opens temporary serial connection). Toggle button placed next to
delete button in card top-right corner.

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

server/src/wled_controller/static/style.css

@@ -263,6 +263,39 @@ section {
 }
 
 
+.card-top-actions {
+    position: absolute;
+    top: 8px;
+    right: 8px;
+    display: flex;
+    align-items: center;
+    gap: 2px;
+}
+
+.card-top-actions .card-remove-btn {
+    position: static;
+}
+
+.card-power-btn {
+    background: none;
+    border: none;
+    color: #777;
+    font-size: 1rem;
+    width: 28px;
+    height: 28px;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    cursor: pointer;
+    border-radius: 4px;
+    transition: color 0.2s, background 0.2s;
+}
+
+.card-power-btn:hover {
+    color: var(--primary-color);
+    background: rgba(76, 175, 80, 0.1);
+}
+
 .card-remove-btn {
     position: absolute;
     top: 10px;