chore: add system metrics

backend/docs/swagger.yaml

@@ -374,6 +374,33 @@ definitions:
         example: agent-001
         type: string
     type: object
+  internal_handlers.AgentSystemMetricsOut:
+    properties:
+      connected_at:
+        example: "2026-04-04 10:30:00"
+        type: string
+      cpu_percent:
+        example: 45.2
+        type: number
+      disk_percent:
+        example: 78.9
+        type: number
+      id:
+        example: agent-001
+        type: string
+      label:
+        example: web-server-1
+        type: string
+      memory_percent:
+        example: 62.5
+        type: number
+      network_rx_bytes:
+        example: 1048576
+        type: number
+      network_tx_bytes:
+        example: 524288
+        type: number
+    type: object
   internal_handlers.CheckCmdIn:
     properties:
       command:
@@ -619,6 +646,26 @@ paths:
       summary: Create registration token
       tags:
       - agents
+  /agents/system-metrics:
+    get:
+      consumes:
+      - application/json
+      description: Returns CPU, RAM, disk, and network usage metrics for all connected
+        agents
+      produces:
+      - application/json
+      responses:
+        "200":
+          description: OK
+          schema:
+            items:
+              $ref: '#/definitions/internal_handlers.AgentSystemMetricsOut'
+            type: array
+      security:
+      - Bearer: []
+      summary: Get agent system metrics
+      tags:
+      - agents
   /auth/login:
     post:
       consumes: