feat: make it possible to see which version is actually running

"I have updated and restarted, but I cannot tell whether it worked" is
not a question the panel could answer. The version was on the startup
line and in the settings page, and nowhere you can reach from outside.

/healthz carries it now. That is the one endpoint answering without a
session, which makes it the only way to ask the question from a terminal
or from the panel itself. The "listening" line repeats it too, because
that is the line the Rune's done_regex matches and therefore the one
sitting at the bottom of the console after a deploy.

The update notice could also never have worked. It reads GitHub's
releases/latest, and this repository had only tags — a tag is not a
release, and that endpoint answers 404 for a repository without any. The
release workflow creates one now, after the image is pushed so a release
never announces a version that failed to build.

VERDANDE_UPDATE_CHECK is a Rune variable, so it can be switched on
without editing the container. Still off by default: it is an outbound
request, and that is a choice to make rather than a default to inherit.

Rune version 1 -> 2, so the panel offers the update.

Note that the check still cannot see anything while the repository is
private — releases/latest is 404 anonymously, exactly as the GHCR package
was. Making the repo public, or teaching the check to carry a token, is a
separate decision.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

rune/verdande.yaml

@@ -11,7 +11,7 @@ gameskill:
     invites and reminders, then start it and open the URL to create the first
     admin account.
   author: "kristianwind"
-  version: 1
+  version: 2
   icon: "app"
 
   # The image is distroless — no shell — so keep_entrypoint runs the binary the
@@ -70,6 +70,14 @@ gameskill:
       pattern: '^[0-9]+(ns|us|ms|s|m|h)$'
       hint: "must be a duration like 720h, 30m or 45s"
 
+    # Off by default because it is an outbound request nobody asked for. It sends
+    # no identifier and reads one public URL — GitHub's releases API — but that is
+    # a choice to make rather than a default to inherit.
+    - key: VERDANDE_UPDATE_CHECK
+      name: "Look for new releases (asks GitHub once a day; sends nothing about you)"
+      type: bool
+      default: false
+
   install:
     # The image has no shell, so the install step borrows one. It only has to make
     # the directory layout exist; verdande creates and migrates its own database on