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>