feat(windows): register development accessibility app

[inayayousfi]

Written by @inayayousfi, typed by GPT-5.6 Sol running in OpenCode.
Every call here is @inayayousfi's, and no agent acted on its own.

Summary

• Register the development build as one Windows accessibility application without alternate launch arguments.
• Keep one elevated helper alive through verification, reducing installation to one UAC prompt while preserving commit and rollback.
• Preserve existing accessibility configuration during installation, rollback, and uninstall.
• Document the registration and add packaging coverage for its required values.

Testing

• QT_QPA_PLATFORM=offscreen .venv-windows/Scripts/python.exe -m unittest discover -s tests
• .venv-windows/Scripts/python.exe with flake8 --select=F,E9,W6 src
• Windows PowerShell parser over packaging/windows/*.ps1
• git diff --check
• Real Windows install, uninstall, and reinstall
• Forced rollback during an update
• Registry, signature, UIAccess token, process, and transaction residue checks

Remaining validation

Windows must reload the accessibility configuration after sign-out. Login, lock, and UAC desktop startup still need validation after that reload.