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/test_helpers_test.go

@@ -0,0 +1,15 @@
+package v1
+
+import "testing"
+
+// setupTestAPI creates a minimal API for testing Central handlers.
+func setupTestAPI(t *testing.T) (*API, string) {
+	tmpDir := t.TempDir()
+
+	api, err := NewAPI(tmpDir, "", nil)
+	if err != nil {
+		t.Fatalf("Failed to create test API: %v", err)
+	}
+
+	return api, tmpDir
+}