feat: Extract Wild Central as standalone Go service

Extract the Central networking functionality from wild-cloud/api into
a standalone service. Wild Central manages DNS (dnsmasq), gateway
(HAProxy), firewall (nftables), VPN (WireGuard), TLS (certbot),
security (CrowdSec), and DDNS — all the network appliance concerns.

All Cloud-specific code (instances, clusters, nodes, apps, backups,
operations, kubectl/talosctl tooling) has been removed. The API struct
and route registration contain only Central endpoints. Tests updated
to match the new API signature.

Builds and all tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/network/detect.go

@@ -0,0 +1,104 @@
+package network
+
+import (
+	"fmt"
+	"net"
+	"os/exec"
+	"strings"
+)
+
+// NetworkInfo holds detected network configuration
+type NetworkInfo struct {
+	PrimaryIP        string `json:"primary_ip"`
+	PrimaryInterface string `json:"primary_interface"`
+	Gateway          string `json:"gateway"`
+}
+
+// DetectNetworkInfo detects the machine's primary network configuration
+// It finds the interface and IP used for internet-bound traffic by checking
+// the route to a public DNS server (8.8.8.8)
+func DetectNetworkInfo() (*NetworkInfo, error) {
+	// Use ip route to find the default route interface and IP
+	// This tells us which interface would be used to reach the internet
+	cmd := exec.Command("ip", "route", "get", "8.8.8.8")
+	output, err := cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get network route: %w", err)
+	}
+
+	line := string(output)
+	// Example output: "8.8.8.8 via 192.168.8.1 dev wlan0 src 192.168.8.152 uid 1000"
+
+	// Extract gateway (after "via")
+	gateway := ""
+	if idx := strings.Index(line, "via "); idx != -1 {
+		rest := line[idx+4:]
+		parts := strings.Fields(rest)
+		if len(parts) > 0 {
+			gateway = parts[0]
+		}
+	}
+
+	// Extract interface (after "dev")
+	iface := ""
+	if idx := strings.Index(line, "dev "); idx != -1 {
+		rest := line[idx+4:]
+		parts := strings.Fields(rest)
+		if len(parts) > 0 {
+			iface = parts[0]
+		}
+	}
+
+	// Extract source IP (after "src")
+	// This is the IP that would be used as the source for outbound traffic
+	ip := ""
+	if idx := strings.Index(line, "src "); idx != -1 {
+		rest := line[idx+4:]
+		parts := strings.Fields(rest)
+		if len(parts) > 0 {
+			ip = parts[0]
+		}
+	}
+
+	if ip == "" || iface == "" {
+		return nil, fmt.Errorf("could not detect network information from route output: %s", line)
+	}
+
+	return &NetworkInfo{
+		PrimaryIP:        ip,
+		PrimaryInterface: iface,
+		Gateway:          gateway,
+	}, nil
+}
+
+// ResolveDomain resolves a domain name to an IP address using the system DNS resolver
+func ResolveDomain(domain string) (string, error) {
+	ips, err := net.LookupIP(domain)
+	if err != nil {
+		return "", fmt.Errorf("failed to resolve domain: %w", err)
+	}
+
+	if len(ips) == 0 {
+		return "", fmt.Errorf("no IP addresses found for domain")
+	}
+
+	// Return the first IPv4 address
+	for _, ip := range ips {
+		if ipv4 := ip.To4(); ipv4 != nil {
+			return ipv4.String(), nil
+		}
+	}
+
+	// If no IPv4, return first IP
+	return ips[0].String(), nil
+}
+
+// GetWildCentralIP returns the IP address of the Wild Central server
+// This is the primary IP address that the server uses for network communication
+func GetWildCentralIP() (string, error) {
+	netInfo, err := DetectNetworkInfo()
+	if err != nil {
+		return "", fmt.Errorf("failed to detect Wild Central IP: %w", err)
+	}
+	return netInfo.PrimaryIP, nil
+}