Fixes#31291
# Checklist for submitter
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.
## Testing
- [x] QA'd all new/changed functionality manually
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
- New Features
- Linux lock now switches Ubuntu + GDM systems to text mode to avoid GUI
issues.
- Persistent lock message is shown and survives reboots.
- Unlock restores the original GUI mode automatically when applicable.
- Bug Fixes
- Prevents black-screen behavior on Ubuntu + GDM after locking by
rebooting to text mode.
- Ensures lock message consistently appears across sessions.
- Improves reliability of session handling during lock/unlock.
- Chores
- Added change note describing the updated Linux lock behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
