feat: add build-stamped version with --version flag and TUI header

Introduce tui.Version (defaults to "dev"), stamped at build time via a
VERSION_LDFLAG in the Makefile (-X .../internal/tui.Version=$(VERSION))
across all build targets. main.go handles "--version"/"-v" before
launching the TUI, and the version is shown next to the title in the
header. Docs updated (README + CLAUDE).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/main.go

@@ -9,6 +9,14 @@ import (
 )
 
 func main() {
+	if len(os.Args) > 1 {
+		switch os.Args[1] {
+		case "--version", "-v":
+			fmt.Println("app-dono installer", tui.Version)
+			return
+		}
+	}
+
 	p := tea.NewProgram(tui.InitialModel())
 	if _, err := p.Run(); err != nil {
 		fmt.Fprintf(os.Stderr, "error: %v\n", err)