Add built-in updater, bump to 1.2.0

- predatord checks the Gitea releases every 6 hours, downloads the
  newest pacman package, verifies its SHA-256 from the release notes
  and installs it with `pacman -U` in a separate systemd unit
- Update notice and install button on the System page, in the sidebar
  and in the panel widget; `predatorctl update [--check] [--yes]`
- Optional API token for private repositories
- packaging/release.py builds and publishes releases in the format
  the updater expects

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

kernel/dkms.conf

@@ -1,5 +1,5 @@
 PACKAGE_NAME="predator-wmi"
-PACKAGE_VERSION="1.1.0"
+PACKAGE_VERSION="1.2.0"
 BUILT_MODULE_NAME[0]="predator_wmi"
 DEST_MODULE_LOCATION[0]="/kernel/drivers/platform/x86"
 MAKE[0]="make KVER=${kernelver} KDIR=${kernel_source_dir}"