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>

server/index.js

@@ -76,6 +76,19 @@ const __dirname = getModuleDir(import.meta.url);
 // Resolving the app root once keeps every repo-level lookup below aligned across both layouts.
 const APP_ROOT = findAppRoot(__dirname);
 const installMode = fs.existsSync(path.join(APP_ROOT, '.git')) ? 'git' : 'npm';
+// Version of the code that is actually running, captured once at process
+// startup. This intentionally does NOT re-read package.json per request: after
+// an update replaces the files on disk, package.json reflects the NEW version
+// while this long-lived process still runs the OLD code. The frontend bundle is
+// rebuilt on update, so a mismatch between this value and the frontend's
+// build-time version means the server was updated but not restarted.
+const RUNNING_VERSION = (() => {
+    try {
+        return JSON.parse(fs.readFileSync(path.join(APP_ROOT, 'package.json'), 'utf8')).version || null;
+    } catch {
+        return null;
+    }
+})();
 const MAX_FILE_UPLOAD_SIZE_MB = 200;
 const MAX_FILE_UPLOAD_SIZE_BYTES = MAX_FILE_UPLOAD_SIZE_MB * 1024 * 1024;
 const MAX_FILE_UPLOAD_COUNT = 20;
@@ -156,7 +169,8 @@ app.get('/health', (req, res) => {
     res.json({
         status: 'ok',
         timestamp: new Date().toISOString(),
-        installMode
+        installMode,
+        version: RUNNING_VERSION
     });
 });