Show the running version on Settings > General

The General page ends with a Version block naming the release this
server runs, so an update can be confirmed from the app.

The version is COBBLE_VERSION, the release tag the image was built with
(Dockerfile ARG, passed by the release workflow, which falls back to
package.json's version on a workflow-dispatch build), else package.json's
version, which a development server reports too, with (development)
after it. runningVersion (src/utils/running-version.ts) drops an
unusable version string rather than showing it.

Also includes the working tree's pending signup guard in
src/pages/__root.server.ts: a user who still holds a session while the
install has no users is sent to /auth/logout (and may load it).

RELEASING.md

@@ -25,7 +25,9 @@ The repository starts private and is made public at the launch gate below.
        - rerun with no changes: reports up to date, no restart
        - update to a new tag: backup taken, data intact
        - `--uninstall` keeps data, `--uninstall --purge` removes it
-5. [ ] Update the version if the release changes it.
+5. [ ] Update the version if the release changes it, including
+       `package.json`'s `version` (the image reports it on Settings > General
+       when it isn't built from a release tag).
 6. [ ] Tag and publish a GitHub release:
 
        git tag v0.1.0