[Cutter81]

Summary

• Harden the PowerShell startup retry loop so transient storage-query failures are logged and do not skip watcher setup.
• Add a task-registration failure recovery path: attempt to restore the previous target script or remove a newly created one, and save preferences only after task registration succeeds.
• Correct README drive-letter safety wording, download guidance, and the limits of Check Status.
• Add TESTING.md with a manual Windows checklist for install/update recovery, occupied letters, protected partitions, offline disks, hot-plug, logging, and release packaging.
• Extend GitHub Actions to validate PowerShell syntax, compile the C# manager, package the ZIP, and run on pull requests.

Validation

• C# compilation/package workflow has passed on the code and documentation updates so far: https://github.com/Cutter81/PersistentSD/actions/runs/39201808570
• The latest workflow change adds a PowerShell parser check; verify its run before merging.
• The workflow checks syntax, compilation, and packaging only. Real drive-letter assignment, hot-plug behavior, and failed-install recovery still require testing on Windows using TESTING.md.

This PR intentionally does not modify the existing release asset or the default branch.