fix(web): ask for the restart that makes an update take effect

The update button pulls new code and restarts nothing. There is no systemctl,
restart, reload or reboot anywhere in the 172-line git_pull handler -- it
stashes, pulls, installs changed requirements, re-removes plugins the user had
uninstalled, and returns "Code updated successfully."

Meanwhile both services go on running the code they loaded at boot. So the
display keeps rendering the old build, the web interface keeps serving the old
build, and the user is told the update worked. Nothing on screen suggests
otherwise, and the next reboot is what actually applies it -- whenever that is.

The affordance for this already exists: the restart-pending banner, raised
after main-config saves, with a Restart Now button wired to the display
service. A code update is a stronger reason to show it than a config save is.

The response now reports restart_required, and applyUpdate raises the banner
with wording for a code update rather than a config save. The banner's message
became a parameter and is persisted next to the flag, since it outlives the
page that raised it.

restart_required is only true when the pull actually moved HEAD. "Already up
to date" is a success too, and prompting after a no-op would train users to
dismiss the prompt unread.

This covers the display service, which is what the Restart Now button drives
and what users notice. The web interface still picks up its own new code on
its next restart; restarting it from inside a request it is serving is a
larger change than this one.

Reverting the flag fails the test that a pull which moved HEAD asks for a
restart. 290 tests pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01STMbQE4YctTacQXfbYqKuW

web_interface/templates/v3/base.html

@@ -413,7 +413,8 @@
             <div class="flex items-center justify-between">
                 <div class="flex items-center space-x-3">
                     <i class="fas fa-rotate text-lg"></i>
-                    <span class="text-sm font-medium" aria-live="polite">
+                    <span class="text-sm font-medium" aria-live="polite"
+                          id="restart-pending-text">
                         Configuration saved &mdash; restart the display to apply the changes
                     </span>
                 </div>
@@ -1146,6 +1147,13 @@
             if (data.status === 'success') {
                 document.getElementById('update-banner').style.display = 'none';
                 try { sessionStorage.removeItem('update-sha-dismissed'); } catch(e) {}
+                // The pull replaced files on disk; the running services still
+                // hold the code they loaded at boot. Ask for the restart that
+                // makes the update actually take effect.
+                if (data.restart_required && typeof window.showRestartPending === 'function') {
+                    window.showRestartPending(
+                        'Update installed \u2014 restart the display to run the new code');
+                }
             }
             if (typeof showNotification === 'function') {
                 showNotification(data.message || 'Update complete', data.status || 'success');