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>

internal/tui/view.go

@@ -114,8 +114,10 @@ func (m Model) View() tea.View {
 
 	help := HelpStyle.Render(helpMsg)
 
+	title := TitleStyle.Render(header) + HelpStyle.Render("  v"+Version)
+
 	v := tea.NewView(fmt.Sprintf("\n%s%s\n\n%s\n\n%s%s\n",
-		pad, TitleStyle.Render(header),
+		pad, title,
 		body,
 		pad, help,
 	))