feat(session): admin UI showing online sessions

frontend/static/locales/en.json

@@ -1136,6 +1136,10 @@
       "revoked": "revoked",
       "expired": "expired",
       "active": "active",
+      "online": "online",
+      "idle": "idle",
+      "presence_online_tooltip": "Online — last seen {{ago}}",
+      "presence_idle_tooltip": "Idle — last seen {{ago}}",
       "revoke": "Revoke",
       "empty": "No sessions match the current filter.",
       "revoke_self_confirm": "⚠️  This is YOUR current session. Revoking it will log YOU out immediately and you'll have to sign back in. Continue?",

frontend/static/locales/fr.json

@@ -1269,6 +1269,10 @@
       "revoked": "révoquée",
       "expired": "expirée",
       "active": "actif",
+      "online": "en ligne",
+      "idle": "inactif",
+      "presence_online_tooltip": "En ligne — vue {{ago}}",
+      "presence_idle_tooltip": "Inactif — vue {{ago}}",
       "revoke": "Révoquer",
       "empty": "Aucune session ne correspond au filtre actuel.",
       "revoke_self_confirm": "⚠️  Il s'agit de VOTRE session actuelle. La révoquer vous déconnectera immédiatement et vous devrez vous reconnecter. Continuer ?",