Complete the remaining ScreenTools roadmap

[rancy777]

@schvarts1, thank you for the work so far. Since I do not have time to continue maintaining ScreenTools, I would like you to take ownership of completing the remaining roadmap.

Please complete and close the remaining work tracked in:

• Implement reliable Windows system-audio loopback capture #1 — reliable Windows system-audio loopback capture and real hardware validation
• Build a recording stability and pause/resume validation matrix #2 — recording stability, pause/resume, long-run and cleanup validation
• Validate instant replay duration, performance, and recording concurrency #3 — instant replay duration, performance and recording-concurrency validation
• Test and fix multi-monitor and high-DPI capture behavior #4 — multi-monitor and high-DPI validation
• REMAINING_WORK.md — output rules, runtime UX, shortcut/environment validation, code cleanup, packaging and release

Expected working rules:

1. Please confirm here whether you are willing to take ownership of the remaining roadmap and provide a proposed order of work.
2. Use focused pull requests instead of pushing large unreviewed batches directly to main.
3. Add a Windows GitHub Actions workflow for build and tests. It must use the pull_request event, minimum read-only permissions, and no repository secrets. Do not use pull_request_target for running contributed code.
4. Each PR should include the actual remote CI result and relevant validation evidence. For hardware-dependent work, document Windows version, displays/DPI, audio devices and test steps.
5. Do not mark an issue complete until its acceptance criteria have been demonstrated.
6. Finish with a documented, reproducible GitHub Release process and an honest list of any remaining limitations.

The priority is reliability and validation, not adding more features. Please use this issue as the overall progress tracker and link the focused PRs here.

[schvarts1]

I will im just occupied rn. Im even correcting some of m'y errors.