feat: add Quiver Launcher parser

[rombat]

Adds a Quiver Launcher parser. Quiver Launcher is an actively maintained fork of GitHub Launcher: same apps.json / settings.json library format, but it has diverged since (saved executable choice, incomplete install marker, new library location in 3.x), so it gets its own parser and existing GitHub Launcher configs stay untouched.

• Resolves each app folder like Quiver does: installPath (apps installed outside Quiver), otherwise AppsPath or the default Apps folder
• Picks the executable like Quiver does: saved choice in selected_executable.txt, then top-level .exe/.bat/.cmd, then a recursive search
• Several executables and no saved choice: the app is skipped with a message asking to pick one in Quiver, rather than guessing (on my library, "largest exe" would have picked a 477 MB patcher instead of the game)
• Not installed or incomplete installs are reported in the failed list
• Windows only for now, like the GitHub Launcher parser. Preset, docs and README row included

f7512e0 is your 34d9c2d ("fix github launcher mistake") cherry-picked from feat/compatibility-switcher: on current master, the exported resolveGithubLauncherGameDir makes the parser registry throw (getParserInfo is not a function), so the app can't be tested without it. Happy to drop it if you'd rather merge that branch first.

Tested on Windows 11 with my real Quiver 3.4.5 library, with apps both in Quiver's Apps folder and in custom install paths: correct executables picked, several-executables and not-installed apps reported as expected.

Closes #895