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/firewall_rule.go

@@ -0,0 +1,17 @@
+package models
+
+import "time"
+
+type FirewallRule struct {
+	ID        int64     `gorm:"primaryKey"          json:"id"`
+	Chain     string    `gorm:"column:chain"        json:"chain"`
+	Priority  int       `gorm:"column:priority"     json:"priority"`
+	MatchExpr string    `gorm:"column:match_expr"   json:"match_expr"`
+	Action    string    `gorm:"column:action"       json:"action"`
+	Comment   *string   `gorm:"column:comment"      json:"comment,omitempty"`
+	Active    bool      `gorm:"column:active"       json:"active"`
+	CreatedAt time.Time `gorm:"column:created_at"   json:"created_at"`
+	UpdatedAt time.Time `gorm:"column:updated_at"   json:"updated_at"`
+}
+
+func (FirewallRule) TableName() string { return "firewall_rules" }