feat(version): warn when the server was updated but not restarted (#898)

When the package is updated on disk but the long-lived server process is
not restarted, the new frontend bundle (served from disk) talks to the
old running backend. New DB-backed features then fail silently — e.g.
deleting/archiving a session appears to do nothing — because the new
schema/routes only take effect on restart.

Nothing currently detects this skew: useVersionCheck only compares the
frontend's build-time version against the latest GitHub release.

This exposes the running server's version (captured once at startup) via
/health, compares it to the frontend's build-time version in
useVersionCheck, and shows a "restart required" banner in the sidebar
(and a small indicator in the collapsed sidebar) when they differ.

- server: add `version` (RUNNING_VERSION, read once at startup) to /health
- useVersionCheck: return `restartRequired` / `runningVersion`
- SidebarFooter / SidebarCollapsed: surface a restart-required banner
- i18n: add `version.restartRequired` to all 10 sidebar locales

Verified with `tsc --noEmit` (client + server) and eslint.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Simos Mikelatos <simosmik@gmail.com>

src/components/sidebar/view/subcomponents/SidebarContent.tsx

@@ -141,6 +141,7 @@ type SidebarContentProps = {
   onCreateProject: () => void;
   onCollapseSidebar: () => void;
   updateAvailable: boolean;
+  restartRequired: boolean;
   releaseInfo: ReleaseInfo | null;
   latestVersion: string | null;
   currentVersion: string;
@@ -178,6 +179,7 @@ export default function SidebarContent({
   onCreateProject,
   onCollapseSidebar,
   updateAvailable,
+  restartRequired,
   releaseInfo,
   latestVersion,
   currentVersion,
@@ -553,6 +555,7 @@ export default function SidebarContent({
 
       <SidebarFooter
         updateAvailable={updateAvailable}
+        restartRequired={restartRequired}
         releaseInfo={releaseInfo}
         latestVersion={latestVersion}
         currentVersion={currentVersion}