feat: allow restrict Pomodoro via password

- introduce password flag in server command line options
- update clientCommand model
- add password requirement for controlling the Pomodoro timer
- document password in README

pkg/models/client.go

@@ -8,8 +8,9 @@ import (
 
 // ClientCommand represents a command from the client (start/stop).
 type ClientCommand struct {
-	Command string                 `json:"command"`
-	Config  GoTomatoPomodoroConfig `json:"config"`
+	Command  string                 `json:"command"`  // comman send to the server
+	Password string                 `json:"password"` // pomodoro control password
+	Config   GoTomatoPomodoroConfig `json:"config"`   // pomodoro config
 }
 
 type Client struct {