Initial commit: Caddy SIP Guardian module

Layer 4 SIP protection with:
- SIP traffic matching (REGISTER, INVITE, etc.)
- Rate limiting and automatic IP banning
- Attack pattern detection (sipvicious, friendly-scanner)
- CIDR whitelisting
- Admin API for ban management

registry.go

@@ -0,0 +1,60 @@
+package sipguardian
+
+import (
+	"sync"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+// Global registry to share guardian instances across modules
+var (
+	guardianRegistry = make(map[string]*SIPGuardian)
+	registryMu       sync.RWMutex
+)
+
+// GetOrCreateGuardian returns a shared guardian instance by name
+func GetOrCreateGuardian(ctx caddy.Context, name string) (*SIPGuardian, error) {
+	if name == "" {
+		name = "default"
+	}
+
+	registryMu.Lock()
+	defer registryMu.Unlock()
+
+	if g, exists := guardianRegistry[name]; exists {
+		return g, nil
+	}
+
+	// Create new guardian
+	g := &SIPGuardian{}
+	if err := g.Provision(ctx); err != nil {
+		return nil, err
+	}
+
+	guardianRegistry[name] = g
+	return g, nil
+}
+
+// GetGuardian returns an existing guardian instance
+func GetGuardian(name string) *SIPGuardian {
+	if name == "" {
+		name = "default"
+	}
+
+	registryMu.RLock()
+	defer registryMu.RUnlock()
+
+	return guardianRegistry[name]
+}
+
+// ListGuardians returns all guardian names
+func ListGuardians() []string {
+	registryMu.RLock()
+	defer registryMu.RUnlock()
+
+	names := make([]string, 0, len(guardianRegistry))
+	for name := range guardianRegistry {
+		names = append(names, name)
+	}
+	return names
+}