fix(gui): don't let minimize-to-tray block app quit and OS shutdown

[esrever10]

Fixes #239.

Problem

With Minimize to tray enabled, the main window's close handler calls e.preventDefault() unconditionally. app.quit() closes all windows before quitting, so the prevented close aborts the whole quit flow: Cmd+Q and the menu Quit just hide the window, and on macOS the app blocks system shutdown/restart until it is force-quit. See #239 for full details.

Fix

The standard Electron pattern for tray apps:

• add a module-level isQuitting flag, set in before-quit and in before-quit-for-update (on macOS autoUpdater.quitAndInstall() closes windows before before-quit fires, so without the latter the interceptor would still block update restarts)
• the close interceptor returns early when isQuitting is set, so windows close and quit proceeds
• drop the removeAllListeners('close') workaround from the two tray Quit items (createTray / rebuildTrayMenu) — app.quit() now works on its own

Behavior is otherwise unchanged: clicking the window's close button with minimize-to-tray enabled still hides to tray.

Testing

• electron-vite build passes
• vitest run: 2054 tests pass (the two electron-binary-dependent test files don't run in my environment; unrelated to this change)
• Manually verified the quit flow logic against Electron's documented before-quit → window close ordering; with the flag set the interceptor no longer prevents close, so Cmd+Q, Dock → Quit, tray → Quit, and OS shutdown all proceed

🤖 Generated with Claude Code

[dbfx]

Thank you @esrever10 !