Fix Windows toast notifications when unfocused

[CaoeUU]

Fixed #3

Problem

Windows toast notifications were not displayed.

Root cause

1. The PowerShell here-string used to construct the toast XML was joined
   onto a single line, causing UnexpectedCharactersAfterHereStringHeader.
2. CreateToastNotifier used the unregistered AppUserModelID
   Codex Notifier. Stable VS Code is registered as
   Microsoft.VisualStudioCode.

The notification subprocess ignored its error, so the failure was silent.

Changes

• Constructed the toast XML with a valid single-quoted PowerShell string.
• Corrected the VS Code AppUserModelID for Windows.

Verification

• Reproduced the original PowerShell parser error.
• Confirmed Microsoft.VisualStudioCode using Get-StartApps.
• Verified that the notification appears while VS Code is unfocused.
• Ran npm run ci.

Compatibility note

This AppUserModelID targets stable Visual Studio Code. VS Code Insiders or
other distributions may require separate AppUserModelID handling.

[zis3c]

Thanks a lot for this PR. This fix was really helpful and matched an issue we had already received before. We have now merged it into our codebase, tested it, and shipped it in v0.1.10. Really appreciate the contribution and the help in improving Codex Notifier.