feat(backend): implement service monitor proto & connect it to http /agents

backend/docs/swagger.json

@@ -12,6 +12,9 @@
                     }
                 ],
                 "description": "Returns a list of all agents currently connected via Collector (log streaming)",
+                "consumes": [
+                    "application/json"
+                ],
                 "produces": [
                     "application/json"
                 ],
@@ -1955,19 +1958,30 @@
             "type": "object",
             "properties": {
                 "connected_at": {
-                    "type": "string"
+                    "description": "Time when agent connected (RFC3339-like)",
+                    "type": "string",
+                    "example": "2026-04-04 10:30:00"
                 },
                 "label": {
-                    "type": "string"
+                    "description": "Human-readable label",
+                    "type": "string",
+                    "example": "web-server-1"
                 },
                 "services": {
+                    "description": "List of services with status (format: \"name:status\")",
                     "type": "array",
                     "items": {
                         "type": "string"
-                    }
+                    },
+                    "example": [
+                        "nginx:running",
+                        "redis:up"
+                    ]
                 },
                 "token": {
-                    "type": "string"
+                    "description": "Unique agent identifier",
+                    "type": "string",
+                    "example": "agent-001"
                 }
             }
         },