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/SidebarCollapsed.tsx

@@ -1,4 +1,4 @@
-import { Settings, Sparkles, PanelLeftOpen, Bug } from 'lucide-react';
+import { Settings, Sparkles, PanelLeftOpen, Bug, AlertTriangle } from 'lucide-react';
 import type { TFunction } from 'i18next';
 
 const DISCORD_INVITE_URL = 'https://discord.gg/buxwujPNRE';
@@ -16,6 +16,7 @@ type SidebarCollapsedProps = {
   onExpand: () => void;
   onShowSettings: () => void;
   updateAvailable: boolean;
+  restartRequired: boolean;
   onShowVersionModal: () => void;
   t: TFunction;
 };
@@ -24,6 +25,7 @@ export default function SidebarCollapsed({
   onExpand,
   onShowSettings,
   updateAvailable,
+  restartRequired,
   onShowVersionModal,
   t,
 }: SidebarCollapsedProps) {
@@ -75,6 +77,18 @@ export default function SidebarCollapsed({
         <DiscordIcon className="h-4 w-4 text-muted-foreground transition-colors group-hover:text-foreground" />
       </a>
 
+      {/* Restart-required indicator */}
+      {restartRequired && (
+        <div
+          className="relative flex h-8 w-8 items-center justify-center rounded-lg"
+          aria-label={t('version.restartRequired')}
+          title={t('version.restartRequired')}
+        >
+          <AlertTriangle className="h-4 w-4 text-amber-500" />
+          <span className="absolute right-1.5 top-1.5 h-1.5 w-1.5 animate-pulse rounded-full bg-amber-500" />
+        </div>
+      )}
+
       {/* Update indicator */}
       {updateAvailable && (
         <button