Add an installer and a tag-driven release pipeline

[sethdtwigg]

Replaces #4, which GitHub auto-closed when its base branch (feat/installer-prerequisites, merged in #3) was deleted. Same branch, same commits, retargeted at master.

Inno Setup installer plus a Release workflow that builds and publishes it.

Update behaviour

The installer updates in place and keeps the old version. It does not uninstall or delete anything.

Where it goes	You choose. The directory page is always shown, and elevation can be picked from the first dialog, so C:\VerseLink or Program Files work as well as the per-user default. The app doesn't need a writable install dir — settings live in %APPDATA%.
Old version	Moved to {app}\previous-versions\VerseLinkWindows-<version>.exe before the new exe is copied in. Rolling back is copying that file back.
Settings	Never touched. They live in %APPDATA%\VerseLink, which the installer neither writes nor removes, and no config.json is shipped.
Running app	Closed before the update, restarted after — so an update doesn't leave you without your hotkey.

Two fixes this required

AppMutex had to go. It only blocks: it tells the user to close the app and aborts if they don't. Under /SILENT that fails outright — Defaulting to Cancel for suppressed message box... Got EAbort exception — and it blocked any install while VerseLink was running anywhere, not just an update of the copy being replaced. PrepareToInstall now closes the app itself and waits for its mutex to clear, with a clear message if it can't within 15s.

WM_CLOSE was broken in the app. It fell through to DefWindowProc, which destroyed the hidden window but left the message loop and worker thread running — the process stayed alive with no window and no tray icon, and Restart Manager had nothing to work with. It now runs the same shutdown path as the tray's Quit, which also fixes sign-out behaviour.

Release pipeline

• A v* tag builds, self-tests, packages and publishes. workflow_dispatch runs the same pipeline without publishing.
• The tag must match Version.h, checked before anything is built, so a release can never advertise a version its binary doesn't report.
• Packaging is gated on --selftest passing.
• A scoped pull_request trigger builds packaging on PRs that touch it — that's what caught the AppMutex failure.

Verified end to end

Against the installer CI produced, on a real machine:

1. install to a chosen (non-default) directory        exit 0
2. start it                                           pid 16832
3. install again over the running copy                exit 0

Asking the running VerseLink to close
Running VerseLink closed after 250 ms
Kept the previous executable as ...\previous-versions\VerseLinkWindows-1.1.0.0.exe

• old version kept, byte-identical to the exe it replaced
• new exe in place
• restarted automatically (pid 16832 → 22560)
• config untouched
• uninstall afterwards left no install dir, no shortcuts, no Add/Remove entry, and kept settings

Honest limitation

A copy that was never installed (an unzipped folder) is invisible to this installer — nothing recorded it, so it's neither updated nor removed. Settings still migrate on first run, but the old folder and any Startup shortcut have to go manually. Called out in the release notes and DISTRIBUTION-NOTES.txt.