feat(db): Phase 1 — DB-Schema, goose-Migrations, GORM-Models

Initialer Schema-Set (8 Migrationen, 13 Tabellen) für EdgeGuard v1:
users + audit_log + system_settings, ha_nodes, backends/domains/
routing_rules/tls_certs, forward_proxy_acls, wireguard_peers,
firewall_rules, dns_zones/dns_records, licenses. Migrations liegen
in internal/database/migrations/ (analog mail-gateway) und werden
per //go:embed ins Binary gepackt — keine separate SQL-Dateien im
.deb. ValidateMigrations + Test schützen vor Duplicate-Versionen
(mail-gateway 2026-05-08-Vorfall). GORM-Models für alle Tabellen,
sensible Felder (password_hash, private_key_enc) sind json:"-".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/models/audit.go

@@ -0,0 +1,18 @@
+package models
+
+import (
+	"encoding/json"
+	"time"
+)
+
+type AuditLog struct {
+	ID        int64           `gorm:"primaryKey"        json:"id"`
+	Actor     string          `gorm:"column:actor"      json:"actor"`
+	Action    string          `gorm:"column:action"     json:"action"`
+	Subject   *string         `gorm:"column:subject"    json:"subject,omitempty"`
+	Detail    json.RawMessage `gorm:"column:detail;type:jsonb" json:"detail,omitempty"`
+	NodeID    *string         `gorm:"column:node_id"    json:"node_id,omitempty"`
+	CreatedAt time.Time       `gorm:"column:created_at" json:"created_at"`
+}
+
+func (AuditLog) TableName() string { return "audit_log" }