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/ha_node.go

@@ -0,0 +1,19 @@
+package models
+
+import "time"
+
+type HANode struct {
+	ID         string     `gorm:"column:id;primaryKey"   json:"id"`
+	Name       string     `gorm:"column:name"            json:"name"`
+	FQDN       string     `gorm:"column:fqdn;uniqueIndex" json:"fqdn"`
+	APIURL     string     `gorm:"column:api_url"         json:"api_url"`
+	PublicIP   *string    `gorm:"column:public_ip;type:inet"   json:"public_ip,omitempty"`
+	InternalIP *string    `gorm:"column:internal_ip;type:inet" json:"internal_ip,omitempty"`
+	Role       string     `gorm:"column:role"            json:"role"`
+	LastSeen   *time.Time `gorm:"column:last_seen"       json:"last_seen,omitempty"`
+	JoinedAt   time.Time  `gorm:"column:joined_at"       json:"joined_at"`
+	CreatedAt  time.Time  `gorm:"column:created_at"      json:"created_at"`
+	UpdatedAt  time.Time  `gorm:"column:updated_at"      json:"updated_at"`
+}
+
+func (HANode) TableName() string { return "ha_nodes" }