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/api/v1/handlers_ddns.go

@@ -0,0 +1,29 @@
+package v1
+
+import (
+	"net/http"
+)
+
+// DDNSStatus returns the current DDNS status (last IP, last update, last error)
+func (api *API) DDNSStatus(w http.ResponseWriter, r *http.Request) {
+	if api.ddns == nil {
+		respondJSON(w, http.StatusOK, map[string]any{
+			"enabled": false,
+			"message": "DDNS not configured",
+		})
+		return
+	}
+	respondJSON(w, http.StatusOK, api.ddns.GetStatus())
+}
+
+// DDNSTrigger forces an immediate DDNS IP check and update
+func (api *API) DDNSTrigger(w http.ResponseWriter, r *http.Request) {
+	if api.ddns == nil {
+		respondError(w, http.StatusServiceUnavailable, "DDNS not configured")
+		return
+	}
+	api.ddns.Trigger()
+	respondJSON(w, http.StatusOK, map[string]string{
+		"message": "DDNS update triggered",
+	})
+}