feat: Refactor CLI API client by splitting billing, carrier, and charging modules into separate files

- Extract Invoice, Payment, Subscriber types and GetInvoices, GetPayments, GenerateInvoice methods to billing.go
- Extract CarrierInfo, ConnectivityStatus, ProfileInfo types and carrier connector methods to carrier.go
- Extract CreditCheckRequest/Response, CreditBalanceResponse types and charging engine methods to charging.go
- Add PacketStats, CreditInfo types and GetPacketStats, GetCreditInfo

apps/cli/internal/api/services.go

@@ -0,0 +1,27 @@
+package api
+
+// Service describes a platform service
+type Service struct {
+	Name    string  `json:"name"`
+	Status  string  `json:"status"`
+	Version string  `json:"version"`
+	Uptime  string  `json:"uptime"`
+	CPU     float64 `json:"cpu"`
+	Memory  string  `json:"memory"`
+}
+
+// PostRestart requests the API to restart the named service.
+func (c *Client) PostRestart(name string) error {
+	return c.doPostJSON("/api/v1/services/"+name+"/restart", nil, nil)
+}
+
+// ListServices returns platform services
+func (c *Client) ListServices() ([]Service, error) {
+	var resp struct {
+		Data []Service `json:"data"`
+	}
+	if err := c.doGetJSON("/api/v1/services", &resp); err != nil {
+		return nil, err
+	}
+	return resp.Data, nil
+}