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/i18n/locales/de/sidebar.json

@@ -115,7 +115,8 @@
     "restoreSessionError": "Fehler beim Wiederherstellen der Sitzung. Bitte erneut versuchen."
   },
   "version": {
-    "updateAvailable": "Update verfügbar"
+    "updateAvailable": "Update verfügbar",
+    "restartRequired": "Update installiert – zum Anwenden Server neu starten"
   },
   "search": {
     "modeProjects": "Projekte",

src/i18n/locales/en/sidebar.json

@@ -115,7 +115,8 @@
     "restoreSessionError": "Error restoring session. Please try again."
   },
   "version": {
-    "updateAvailable": "Update available"
+    "updateAvailable": "Update available",
+    "restartRequired": "Update installed — restart the server to apply"
   },
   "search": {
     "modeProjects": "Projects",

src/i18n/locales/fr/sidebar.json

@@ -115,7 +115,8 @@
     "restoreSessionError": "Erreur lors de la restauration de la session. Veuillez réessayer."
   },
   "version": {
-    "updateAvailable": "Mise à jour disponible"
+    "updateAvailable": "Mise à jour disponible",
+    "restartRequired": "Mise à jour installée — redémarrez le serveur pour l'appliquer"
   },
   "search": {
     "modeProjects": "Projets",

src/i18n/locales/it/sidebar.json

@@ -115,7 +115,8 @@
     "restoreSessionError": "Errore durante il ripristino della sessione. Riprova."
   },
   "version": {
-    "updateAvailable": "Aggiornamento disponibile"
+    "updateAvailable": "Aggiornamento disponibile",
+    "restartRequired": "Aggiornamento installato — riavvia il server per applicarlo"
   },
   "search": {
     "modeProjects": "Progetti",

src/i18n/locales/ja/sidebar.json

@@ -114,7 +114,8 @@
     "restoreSessionError": "セッションの復元でエラーが発生しました。もう一度お試しください。"
   },
   "version": {
-    "updateAvailable": "アップデートあり"
+    "updateAvailable": "アップデートあり",
+    "restartRequired": "更新が適用されていません。サーバーを再起動してください"
   },
   "deleteConfirmation": {
     "deleteProject": "プロジェクトを除去",

src/i18n/locales/ko/sidebar.json

@@ -114,7 +114,8 @@
     "restoreSessionError": "세션 복원 오류. 다시 시도해주세요."
   },
   "version": {
-    "updateAvailable": "업데이트 가능"
+    "updateAvailable": "업데이트 가능",
+    "restartRequired": "업데이트가 설치됨 — 적용하려면 서버를 재시작하세요"
   },
   "deleteConfirmation": {
     "deleteProject": "프로젝트 제거",

src/i18n/locales/ru/sidebar.json

@@ -115,7 +115,8 @@
     "restoreSessionError": "Ошибка при восстановлении сеанса. Попробуйте снова."
   },
   "version": {
-    "updateAvailable": "Доступно обновление"
+    "updateAvailable": "Доступно обновление",
+    "restartRequired": "Обновление установлено — перезапустите сервер для применения"
   },
   "search": {
     "modeProjects": "Проекты",

src/i18n/locales/tr/sidebar.json

@@ -115,7 +115,8 @@
     "restoreSessionError": "Oturum geri yüklenirken hata oluştu. Lütfen tekrar dene."
   },
   "version": {
-    "updateAvailable": "Güncelleme mevcut"
+    "updateAvailable": "Güncelleme mevcut",
+    "restartRequired": "Güncelleme yüklendi — uygulamak için sunucuyu yeniden başlatın"
   },
   "search": {
     "modeProjects": "Projeler",

src/i18n/locales/zh-CN/sidebar.json

@@ -115,7 +115,8 @@
     "restoreSessionError": "恢复会话时出错，请重试。"
   },
   "version": {
-    "updateAvailable": "有可用更新"
+    "updateAvailable": "有可用更新",
+    "restartRequired": "已安装更新 — 请重启服务器以生效"
   },
   "search": {
     "modeProjects": "项目",

src/i18n/locales/zh-TW/sidebar.json

@@ -114,7 +114,8 @@
     "restoreSessionError": "還原工作階段時出錯，請重試。"
   },
   "version": {
-    "updateAvailable": "有可用更新"
+    "updateAvailable": "有可用更新",
+    "restartRequired": "已安裝更新 — 請重新啟動伺服器以套用"
   },
   "search": {
     "modeProjects": "專案",