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

backend/internal/handlers/agents.go

@@ -16,17 +16,19 @@ func NewAgentsGroup(h *Handlers, coll *collector.Collector) AgentsGroup {
 	return AgentsGroup{Handlers: h, collector: coll}
 }
 
+// AgentInfo represents a connected agent's current status.
 type AgentInfo struct {
-	Token       string   `json:"token"`
-	Label       string   `json:"label"`
-	Services    []string `json:"services"`
-	ConnectedAt string   `json:"connected_at"`
+	Token       string   `json:"token" example:"agent-001"`                  // Unique agent identifier
+	Label       string   `json:"label" example:"web-server-1"`               // Human-readable label
+	Services    []string `json:"services" example:"nginx:running,redis:up"`  // List of services with status (format: "name:status")
+	ConnectedAt string   `json:"connected_at" example:"2026-04-04 10:30:00"` // Time when agent connected (RFC3339-like)
 }
 
 // @Summary Get connected agents
 // @Description Returns a list of all agents currently connected via Collector (log streaming)
 // @Tags agents
 // @Security Bearer
+// @Accept json
 // @Produce json
 // @Success 200 {array} AgentInfo
 // @Router /agents [get]