feat v1.29.0: 'new device' flag with a red dot

- auto devices/light groups appearing after install get a server-side 'new'
  flag (settings.new_device_ids) and a red dot top-right of the icon; opening
  the device's editor clears it for every client
- known_devices baseline seeded silently on first run — upgrades never flood
  the plan with dots; hand-made markers never flagged
- pure diffNewDevices + unit tests; backend schema; smoke_new_device.mjs;
  TESTING.md row

src/styles.ts

@@ -526,6 +526,18 @@ export const cardStyles = css`
     @media (prefers-reduced-motion: reduce) {
       .dev.alarm::after { animation: none; opacity: 0.9; }
     }
+    .dev .newdot {
+      position: absolute;
+      top: calc(var(--icon-size, 2.5cqw) * -0.12);
+      right: calc(var(--icon-size, 2.5cqw) * -0.12);
+      width: calc(var(--icon-size, 2.5cqw) * 0.34);
+      height: calc(var(--icon-size, 2.5cqw) * 0.34);
+      border-radius: 50%;
+      background: #f0301f;
+      border: 2px solid var(--card-background-color, var(--hp-bg));
+      pointer-events: none;
+      z-index: 2;
+    }
     .devlayer {
       position: absolute;
       inset: 0;