Add system tray icon, file logging, and fix Windows hotkey conflict

- Adds fyne.io/systray with a programmatic monkey face icon and Quit menu item
- Logs to discord-lobby-mute.log next to the exe so startup errors are visible
  without a console window
- Windows now uses raw Win32 RegisterHotKey in a locked goroutine instead of
  golang.design/x/hotkey, avoiding a deadlock where systray and the hotkey
  library both try to own the main thread message loop
- Build with: GOOS=windows GOARCH=amd64 go build -ldflags "-H windowsgui" -o discord-lobby-mute.exe .

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

go.mod

@@ -9,7 +9,9 @@ require (
 )
 
 require (
+	fyne.io/systray v1.12.1 // indirect
+	github.com/godbus/dbus/v5 v5.1.0 // indirect
 	github.com/gorilla/websocket v1.4.2 // indirect
 	golang.org/x/crypto v0.0.0-20210421170649-83a5a9bb288b // indirect
-	golang.org/x/sys v0.0.0-20201119102817-f84b799fce68 // indirect
+	golang.org/x/sys v0.15.0 // indirect
 )