Releases on Gitea, one-line installer and auto-update (1.1.0)

- .github/workflows/release.yml: a tag vX.Y.Z runs the tests, publishes
  daynivo-kiosk-os-X.Y.Z.tar.gz (+ .sha256) and install-online.sh as a
  Gitea release, then builds the SD image with pi-gen and attaches it.
- install-online.sh: curl | sudo bash installer for the latest release.
- voxip-kiosk-updater: checks the latest release, verifies and unpacks a
  newer one under /opt/daynivo-kiosk-os and runs its update.sh. A daily
  timer checks around 03:00 and installs when auto_update is on.
- Web interface: Systeem -> Software-updates with the auto-update switch,
  check now and install now (helper verbs update-check / update-install).
- CI checks out with plain git, so it runs on Gitea's act_runner too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

bin/voxip-kiosk-updater

@@ -0,0 +1,9 @@
+#!/usr/bin/python3 -I
+# Installed to /usr/lib/voxip-kiosk/ by install.sh. -I: ignore PYTHON* env and user site-packages.
+import sys
+
+sys.path.insert(0, "/usr/lib/voxip-kiosk/python")
+
+from voxip_kiosk.updater import main  # noqa: E402
+
+sys.exit(main())