Turn Weave routing on

When the user invokes $router-on, switch this Codex installation back onto
the Weave Router using the managed configuration already on disk.

Run exactly:

npx --package @weave-os/router -y -- weave-router on --codex{{SCOPE}}

Then report the result and tell the user the change takes effect on their next
codex launch — Codex reads its provider config at startup, so the current
session keeps routing as it already was. Do not re-run the installer or alter
any other Codex settings.