docs(api): update API documentation with new session listing endpoint

feat(session): add API endpoint to list active sessions

docs/api.md

@@ -250,6 +250,55 @@ X-Timestamp: 1704067200000
 
 ---
 
+## List Active Sessions
+
+**Endpoint**: `/sessionMgr/list`  
+**Method**: GET  
+**Auth Required**: Yes (token)  
+**Permission Level**: Superuser, Admin
+
+**Request Headers**:
+```
+X-Token: your_token
+X-Timestamp: 1704067200000
+```
+
+| Header | Type | Required | Description |
+|--------|------|----------|-------------|
+| X-Token | string | Yes | Authentication token |
+| X-Timestamp | int64 | Yes | Client timestamp in milliseconds |
+
+**Response**:
+```json
+{
+  "success": true,
+  "message": "Active sessions listed",
+  "data": [
+    {
+      "ID": "session-5f4dcc3b5aa765d61d8327deb882cf99-1704067200000",
+      "userID": 1,
+      "username": "admin",
+      "expireAt": "2024-01-01T01:00:00Z"
+    },
+    {
+      "ID": "session-7c6a180b36896a0a8c010710c0780347-1704067210000",
+      "userID": 2,
+      "username": "new_user",
+      "expireAt": "2024-01-01T01:00:10Z"
+    }
+  ]
+}
+```
+
+| Field | Type | Description |
+|-------|------|-------------|
+| ID | string | Unique session ID |
+| userID | int | User ID |
+| username | string | Username |
+| expireAt | string | Session expiration time (ISO 8601 format) |
+
+---
+
 ## Create frpc Instance
 
 **Endpoint:** `/frpcAct/instanceMgr/create`  
@@ -541,6 +590,7 @@ X-Timestamp: 1704067200000
 | Modify instance | ✓ | ✓ | ✗ |
 | List instances | ✓ | ✓ | ✓ (limited) |
 | Manage users | ✓ | ✗ | ✗ |
+| List active sessions | ✓ | ✓ | ✗ |
 
 ## Timestamp Validation
 

session.go

@@ -271,7 +271,7 @@ func JoinSession(userID int, userName string, token string) error {
 	}
 
 	sessionMap[sessionID] = session
-	postLog.Info(fmt.Sprintf("[JoinSession] User [%d]%s joined session %s with token %s", userID, userName, sessionID, token))
+	postLog.Debug(fmt.Sprintf("[JoinSession] User [%d]%s joined session %s with token %s", userID, userName, sessionID, token))
 	return nil
 }