feat: add version and protocol version

- define GoTomatoVersion constant for versioning
- add protocol version field to all server messages
- add `-version` cli parameter
- update README

🤖

pkg/models/server.go

@@ -8,4 +8,5 @@ type ServerMessage struct {
 	TimeLeft         int                    `json:"time_left"` // Remaining time in seconds
 	Ongoing          bool                   `json:"ongoing"`   // Ongoing pomodoro
 	Paused           bool                   `json:"paused"`    // Is timer paused
+	GoTomatoVersion  string                 `json:"version"`   // Version of the server
 }