Fix elevated launcher quoting for unusual paths

[css521]

Summary

• move the elevation handoff into a PowerShell helper invoked with -File and a bound -ScriptPath parameter
• quote the child PowerShell.exe argument line using Windows argv rules, preserving spaces, apostrophes, ampersands, parentheses, Unicode, and trailing backslashes
• keep the visible UAC prompt and preview-only behavior; propagate missing-script and elevation failures as non-zero exits
• document the launcher behavior and add regression coverage that does not display UAC

Testing

Run on Windows 11 with Windows PowerShell 5.1:

• Invoke-Pester -Path .\tests\Run-PATH-Repair-Admin.Tests.ps1 — 12 passed, 0 failed
• Invoke-Pester -Path .\tests — 28 passed, 0 failed
• git diff --check — passed

The regression tests cover a path containing spaces, an apostrophe, &, parentheses, and Chinese characters; validate parsing with CommandLineToArgvW; exercise a real non-elevated child process and the CMD-to-PowerShell handoff; and verify missing-target and elevation-failure behavior. Restoring the original batch launcher makes two of the new regression tests fail, confirming they detect the reported bug.

Fixes #5