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/packet.go

@@ -0,0 +1,34 @@
+package api
+
+// Packet Gateway Integration
+type PacketStats struct {
+	IP    uint64 `json:"ip"`
+	Bytes uint64 `json:"bytes"`
+}
+
+type PacketCreditInfo struct {
+	IP     uint64 `json:"ip"`
+	Credit int64  `json:"credit"`
+}
+
+// GetPacketStats retrieves packet statistics
+func (c *Client) GetPacketStats() ([]PacketStats, error) {
+	var resp struct {
+		Data []PacketStats `json:"data"`
+	}
+	if err := c.doGetJSON("/api/v1/packet-gateway/stats", &resp); err != nil {
+		return nil, err
+	}
+	return resp.Data, nil
+}
+
+// GetPacketCreditInfo retrieves credit information from packet gateway
+func (c *Client) GetPacketCreditInfo() ([]PacketCreditInfo, error) {
+	var resp struct {
+		Data []PacketCreditInfo `json:"data"`
+	}
+	if err := c.doGetJSON("/api/v1/packet-gateway/credits", &resp); err != nil {
+		return nil, err
+	}
+	return resp.Data, nil
+}