feat(admin): show active session/users on dashboard

frontend/static/locales/en.json

@@ -836,6 +836,17 @@
     "total_users": "Total Users",
     "active_users": "Active Users",
     "admins": "Admins",
+    "external_users": "External",
+    "external_users_tooltip": "Grant-only accounts — magic-link, OIDC-only, OCM recipients",
+    "online_users": "Online users",
+    "online_users_tooltip": "Distinct users with a session active in the last 5 minutes",
+    "online_sessions": "Online sessions",
+    "online_sessions_tooltip": "Non-revoked sessions active in the last 5 minutes — multi-device users contribute more than one",
+    "section_accounts": "User accounts",
+    "section_activity": "Live activity",
+    "section_system": "System",
+    "live": "live",
+    "live_tooltip": "Reflects sessions active in the last 5 minutes",
     "version": "Version",
     "storage_overview": "Storage Overview",
     "used": "Used",

frontend/static/locales/fr.json

@@ -801,6 +801,17 @@
     "total_users": "Utilisateurs totaux",
     "active_users": "Utilisateurs actifs",
     "admins": "Admins",
+    "external_users": "Externes",
+    "external_users_tooltip": "Comptes invités — magic-link, OIDC seulement, destinataires OCM",
+    "online_users": "Utilisateurs en ligne",
+    "online_users_tooltip": "Utilisateurs distincts ayant une session active dans les 5 dernières minutes",
+    "online_sessions": "Sessions en ligne",
+    "online_sessions_tooltip": "Sessions non révoquées actives dans les 5 dernières minutes — les utilisateurs multi-appareils en contribuent plusieurs",
+    "section_accounts": "Comptes utilisateurs",
+    "section_activity": "Activité en direct",
+    "section_system": "Système",
+    "live": "en direct",
+    "live_tooltip": "Reflète les sessions actives dans les 5 dernières minutes",
     "version": "Version",
     "storage_overview": "Aperçu du stockage",
     "used": "Utilisé",