rexenv 0.8.9

The fixes 0.8.8's release night found, and one the Linux smoke test found after it. Linux: the .rex route routed NOTHING in 0.8.8 — systemd-resolved gives no DNS scope to a link whose only address is link-local, so rexenv0 now carries 192.0.2.53/32 and every .rex answer on a Linux host is rexenv's own; and after an in-app deb update the app comes back — the relauncher runs from the new /usr/bin/rexenv rather than the deleted inode the old process was started from (this is the OLD side of a swap, so 0.8.8 → 0.8.9 still opens by hand once; 0.8.9 onward relaunches). Windows: the handle sweep that made a service inherit nothing now runs once at process start — beside a spawn it cleared other threads' fresh child pipes; the update zip's .sha256 names its file. Every OS: the accepted update serial, bytes and signature are kept per document, so a copy that once read another OS's descriptor no longer refuses its own as a replay; and when a descriptor is refused the About card says so instead of 'couldn't reach the update server'.