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>

main_windows.go

@@ -0,0 +1,5 @@
+//go:build windows
+
+package main
+
+func main() { run() }