feat: add set-window-title command

Set the terminal window title using termenv.

Fixes: #610

commands.go

@@ -170,3 +170,21 @@ func Sequentially(cmds ...Cmd) Cmd {
 		return nil
 	}
 }
+
+// setWindowTitleMsg is an internal message used to set the window title.
+type setWindowTitleMsg string
+
+// SetWindowTitle produces a command that sets the terminal title.
+// The message returned contains the title that was set.
+//
+// For example:
+//
+//	func (m model) Init() Cmd {
+//	    // Set title.
+//	    return tea.SetWindowTitle("My App")
+//	}
+func SetWindowTitle(title string) Cmd {
+	return func() Msg {
+		return setWindowTitleMsg(title)
+	}
+}

screen.go

@@ -167,3 +167,8 @@ func (p *Program) EnableMouseAllMotion() {
 func (p *Program) DisableMouseAllMotion() {
 	p.renderer.disableMouseAllMotion()
 }
+
+// SetWindowTitle sets the terminal window title.
+func (p *Program) SetWindowTitle(title string) {
+	p.output.SetWindowTitle(title)
+}

tea.go

@@ -313,6 +313,9 @@ func (p *Program) eventLoop(model Model, cmds chan Cmd) (Model, error) {
 						p.Send(cmd())
 					}
 				}()
+
+			case setWindowTitleMsg:
+				p.SetWindowTitle(string(msg))
 			}
 
 			// Process internal messages for the renderer.