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/domain.go

@@ -0,0 +1,17 @@
+package models
+
+import "time"
+
+type Domain struct {
+	ID                int64     `gorm:"primaryKey"                  json:"id"`
+	Name              string    `gorm:"column:name;uniqueIndex"     json:"name"`
+	Active            bool      `gorm:"column:active"               json:"active"`
+	PrimaryBackendID  *int64    `gorm:"column:primary_backend_id"   json:"primary_backend_id,omitempty"`
+	HTTPToHTTPS       bool      `gorm:"column:http_to_https"        json:"http_to_https"`
+	HSTSEnabled       bool      `gorm:"column:hsts_enabled"         json:"hsts_enabled"`
+	Notes             *string   `gorm:"column:notes"                json:"notes,omitempty"`
+	CreatedAt         time.Time `gorm:"column:created_at"           json:"created_at"`
+	UpdatedAt         time.Time `gorm:"column:updated_at"           json:"updated_at"`
+}
+
+func (Domain) TableName() string { return "domains" }