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).

Dockerfile

@@ -17,6 +17,12 @@ ENV DATA_DIR=/data
 ENV DB_DIR=/data/db
 ENV BUN_FEATURE_FLAG_DISABLE_STREAMING_INSTALL=1
 
+# The release's version, which Settings > General shows. The release
+# workflow passes the published tag; a local build leaves it empty and
+# the app falls back to `package.json`'s version.
+ARG COBBLE_VERSION=
+ENV COBBLE_VERSION=$COBBLE_VERSION
+
 WORKDIR /app
 
 RUN echo 'alias ll="ls -laF"' >/root/.bashrc