feat(gateway): expand sessions surface with operator metadata and paging hardening

docs/api/PROTOCOL.md

@@ -417,13 +417,19 @@ Useful for proactive compaction monitoring and operator dashboards.
 
 #### `sessions.list`
 
-List all sessions.
+List sessions with optional persisted inclusion, frontend filtering, and paging.
 
 **Request:**
 ```json
 {
   "id": 3,
-  "method": "sessions.list"
+  "method": "sessions.list",
+  "params": {
+    "includePersisted": true,
+    "frontend": "ws",
+    "limit": 50,
+    "offset": 0
+  }
 }
 ```
 
@@ -435,12 +441,27 @@ List all sessions.
     "sessions": [
       {
         "id": "telegram:123456",
-        "createdAt": "2025-02-13T10:00:00Z",
-        "lastActiveAt": "2025-02-13T12:00:00Z",
+        "frontend": "telegram",
+        "userId": "123456",
         "messageCount": 42,
-        "connectionCount": 1
+        "lastMessageAt": 1739448000000,
+        "config": {
+          "modelTier": "fast",
+          "queue": {
+            "mode": "followup",
+            "overflow": "drop_old",
+            "cap": 8,
+            "debounceMs": 250,
+            "summarizeOverflow": true
+          },
+          "elevation": {
+            "active": false,
+            "untilMs": 1739451600000
+          }
+        }
       }
-    ]
+    ],
+    "total": 1
   }
 }
 ```