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

custom_components/houseplan/manifest.json

@@ -16,5 +16,5 @@
   "issue_tracker": "https://github.com/Matysh/houseplan-card/issues",
   "requirements": [],
   "single_config_entry": true,
-  "version": "1.28.1"
+  "version": "1.29.0"
 }