Add remote-chromium.sh and install waypipe in setup-local.sh

Runs Chromium on the home machine with its window drawn on the travel
laptop, so logged-in browser accounts stay on the home machine. Closes
any running instance first, since Chromium's one-process-per-profile
lock would otherwise open the window on the home machine's own screen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -140,6 +140,18 @@ LUKS-encrypted later, this recovery path breaks (nothing starts until
 someone types the disk passphrase locally) unless something like
 `dropbear-initramfs` is added for remote unlock.
 
+## Single remote app: Chromium with your logged-in accounts
+
+`remote-chromium.sh` (run on the travel laptop) closes any Chromium you have
+running on the home machine, then launches it there with its window drawn
+locally via `waypipe` (`--x11` for classic X11 forwarding instead). The close
+step matters: Chromium allows one process per profile, so a still-running
+instance would swallow the new window onto the home machine's own screen.
+Needs `waypipe` on both ends (`setup-local.sh` installs it locally; on the
+home machine: `sudo apt install waypipe`). Untested against Tailscale SSH,
+which may not support the socket/X11 forwarding these rely on - if the
+connection fails, plain OpenSSH is the fix.
+
 ## Gotchas hit while building this (so they don't get re-debugged)
 
 - **`usermod`/`visudo`: command not found** after `su` - not missing, just