docs(faq): document missing video output while the screen is locked

[junkerderprovinz]

Reference the issue numbers and reviewers

#174 @ehfd

Explain relevant issues and how this pull request solves them

This pull request documents the known limitation discussed in #174: when the screen is locked on an existing desktop, Selkies produces no video output. As established in that thread, the display manager's lock switches to a greeter on a separate display or virtual terminal (observed with LightDM spawning a second X server on :1), so Selkies capturing the original DISPLAY loses output until the screen is unlocked. Since documentation was explicitly requested in that issue, this adds a FAQ entry covering the cause and the workarounds. Documents #174; feel free to close that issue if this satisfies the documentation requirement.

Describe the changes in code and its dependencies and justify that they work as intended after testing

Adds one new entry to docs/faq.md, matching the existing entry pattern (## heading, <details markdown> block with an Open Answer summary). It explains why the video output stops on screen lock and lists the workarounds in order: disable screen locking and any autostarted locker (light-locker, xscreensaver, gnome-screensaver), run xset s off -dpms, add Option "HardDPMS" "False" in /etc/X11/xorg.conf for NVIDIA DPMS blanking, or use a container/session without a display manager. Verified that the Markdown renders correctly with the md_in_html extension used for the existing entries: all eight <details>/</details> pairs and summaries are balanced. Documentation-only change; no code or dependencies are affected.

Describe alternatives you've considered

Handling the lock screen transition in code was ruled out in #174 ("There is not much that can be reliably done here"), since the greeter runs on a different display that Selkies cannot follow, so documenting the limitation and workarounds is the agreed approach.

Additional context

The new entry is placed directly after the existing display-manager-related entry ("The web interface refuses to start up in the terminal after rebooting...") to keep session/display-manager topics grouped together.

• I confirm that this pull request is relevant to the scope of this project. If you know that upstream projects are the cause of this problem, please file the pull request there.
• I confirm that this pull request has been tested thoroughly and to the best of my knowledge that additional unintended problems do not arise.
• I confirm that the style of the changed code conforms to the overall style of the project.
• I confirm that I have read other open and closed pull requests and that duplicates do not exist.
• I confirm that I have justified the need for this pull request and that the changes reflect the fix for the specified problem.
• I confirm that no portion of this pull request contains credentials or other private information, and it is my own responsibility to protect my privacy.
• I confirm that the authors of this pull request does not willfully breach or infringe legal regulations, in any and all global law, regarding trademarks, trade names, logos, patents, or any and all other forms of external intellectual property, as well as adhering to software license terms of open-source and proprietary software projects.

[gemini-code-assist]

Code Review

This pull request adds a new FAQ entry to docs/faq.md explaining why video output is lost when the screen is locked on an existing desktop and providing workarounds to avoid this issue. I have no feedback to provide as there are no review comments.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.