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>

hotkey_notwindows.go

@@ -0,0 +1,24 @@
+//go:build !windows
+
+package main
+
+import "golang.design/x/hotkey"
+
+func startHotkey(keybind string) (<-chan struct{}, error) {
+	mods, key, err := parseKeybind(keybind)
+	if err != nil {
+		return nil, err
+	}
+	hk := hotkey.New(mods, key)
+	if err := hk.Register(); err != nil {
+		return nil, err
+	}
+	out := make(chan struct{})
+	go func() {
+		for range hk.Keydown() {
+			out <- struct{}{}
+		}
+		close(out)
+	}()
+	return out, nil
+}