docs: README refresh for v0.2.0 release - Name the current release (v0.2.0, 2026-07-06) at the top of Download and note the in-app updater path for existing installs. - Date-stamp the unsigned-installer explanation (still accurate as of v0.2.0 — the D-U-N-S/cert verification wait is unchanged; the integrity .sig note still holds and each release carries per-bundle signatures).