qSnapper 1.2.3

Updated to version 1.2.3

The "System Rollback" button in the snapshot detail dialog previously called Snapshot::setDefault() directly on the selected snapshot,
which is only correct for transactional-update systems (read-only root).

On a standard openSUSE system with a writable root subvolume, this caused the read-only target snapshot itself to become the default subvolume,
leaving the system unable to boot into a writable state.

Reimplement SnapshotOperations::RollbackSnapshot() to mirror the logic of snapper rollback N
(client/snapper/cmd-rollback.cc):

• Detect the ambit by inspecting whether the previous default snapshot is read-only.

• CLASSIC ambit (writable previous default):

  1. Create a read-only backup snapshot of the current state
     with description "rollback backup of #",
     cleanup="number", userdata["important"]="yes".
  2. Create a writable copy of the target snapshot with
     description "writable copy of #".
  3. If the previous default had an empty cleanup algorithm,
     set it to "number" via modifySnapshot().
  4. Call setDefault() on the newly created writable copy.

• TRANSACTIONAL ambit (read-only previous default):
  Call setDefault() on the target snapshot directly, matching
  the previous behavior for this case.

Both libsnapper >= 7.4 (with Plugins::Report) and older versions are supported via the existing LIBSNAPPER_VERSION_AT_LEAST macro,
and logPluginReport() is invoked after each plugin-aware call.

The GUI side (SnapshotListModel, SnapperService, QML) and the D-Bus interface signature (RollbackSnapshot(int)) are unchanged,
so no client-side changes or polkit action updates are required.

SELinux policy updates (selinux/qsnapper.te):

• Allow qsnapper_dbus_t to execute snapper_grub_plugin_exec_t, required by libsnapper to invoke /usr/lib/snapper/plugins/grub
  during setDefault()/rollback for bootloader entry updates.

• Allow qsnapper_t to read passwd_file_t and access systemd_userdbd_runtime_t for user name resolution during GUI
  startup (pre-existing denials surfaced during rollback testing).

Full Changelog: v1.2.2...v1.2.3