feat(fw): Models + Repos für Firewall-v2 (6 Entities)

Models (internal/models/):
* FirewallAddressObject (host|network|range|fqdn)
* FirewallAddressGroup mit MemberIDs gorm:"-"-Slice
* FirewallService (proto+ports, builtin-Flag)
* FirewallServiceGroup mit MemberIDs
* FirewallRule (v2-Shape, src/dst nullable refs, exactly-one-of-Validation
  in Handler-Layer)
* FirewallNATRule (kind=dnat|snat|masquerade, alle nullable)

Repos (internal/services/firewall/, ein Paket):
* AddressObjectsRepo, AddressGroupsRepo (mit Members-Junction-Ops)
* ServicesRepo (refused Update/Delete für builtin=TRUE Rows),
  ServiceGroupsRepo
* RulesRepo, NATRulesRepo
Jeweils Standard-CRUD; Group-Repos handhaben Members atomic in einer
TX (Update ersetzt komplette Membership).

Handler + Renderer-Rewrite + Frontend folgen in den nächsten
Commits.

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

internal/services/firewall/services.go

@@ -0,0 +1,113 @@
+package firewall
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"git.netcell-it.de/projekte/edgeguard-native/internal/models"
+)
+
+var ErrServiceNotFound = errors.New("service not found")
+
+type ServicesRepo struct {
+	Pool *pgxpool.Pool
+}
+
+func NewServicesRepo(pool *pgxpool.Pool) *ServicesRepo { return &ServicesRepo{Pool: pool} }
+
+const svcBaseSelect = `
+SELECT id, name, proto, port_start, port_end, builtin, description,
+       created_at, updated_at
+FROM firewall_services
+`
+
+func (r *ServicesRepo) List(ctx context.Context) ([]models.FirewallService, error) {
+	rows, err := r.Pool.Query(ctx, svcBaseSelect+" ORDER BY name ASC")
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := make([]models.FirewallService, 0, 16)
+	for rows.Next() {
+		s, err := scanService(rows)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, *s)
+	}
+	return out, rows.Err()
+}
+
+func (r *ServicesRepo) Get(ctx context.Context, id int64) (*models.FirewallService, error) {
+	row := r.Pool.QueryRow(ctx, svcBaseSelect+" WHERE id = $1", id)
+	s, err := scanService(row)
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, ErrServiceNotFound
+		}
+		return nil, err
+	}
+	return s, nil
+}
+
+func (r *ServicesRepo) Create(ctx context.Context, s models.FirewallService) (*models.FirewallService, error) {
+	row := r.Pool.QueryRow(ctx, `
+INSERT INTO firewall_services (name, proto, port_start, port_end, builtin, description)
+VALUES ($1, $2, $3, $4, FALSE, $5)
+RETURNING id, name, proto, port_start, port_end, builtin, description, created_at, updated_at`,
+		s.Name, s.Proto, s.PortStart, s.PortEnd, s.Description)
+	return scanService(row)
+}
+
+func (r *ServicesRepo) Update(ctx context.Context, id int64, s models.FirewallService) (*models.FirewallService, error) {
+	// Forbid editing builtin services — they're guaranteed by the
+	// migration set; users that want a tweak can clone with a new name.
+	cur, err := r.Get(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	if cur.Builtin {
+		return nil, errors.New("builtin service cannot be edited — clone it under a new name")
+	}
+	row := r.Pool.QueryRow(ctx, `
+UPDATE firewall_services SET
+   name = $1, proto = $2, port_start = $3, port_end = $4,
+   description = $5, updated_at = NOW()
+WHERE id = $6
+RETURNING id, name, proto, port_start, port_end, builtin, description, created_at, updated_at`,
+		s.Name, s.Proto, s.PortStart, s.PortEnd, s.Description, id)
+	return scanService(row)
+}
+
+func (r *ServicesRepo) Delete(ctx context.Context, id int64) error {
+	cur, err := r.Get(ctx, id)
+	if err != nil {
+		return err
+	}
+	if cur.Builtin {
+		return errors.New("builtin service cannot be deleted")
+	}
+	tag, err := r.Pool.Exec(ctx, `DELETE FROM firewall_services WHERE id = $1`, id)
+	if err != nil {
+		return err
+	}
+	if tag.RowsAffected() == 0 {
+		return ErrServiceNotFound
+	}
+	return nil
+}
+
+func scanService(row interface{ Scan(...any) error }) (*models.FirewallService, error) {
+	var s models.FirewallService
+	if err := row.Scan(
+		&s.ID, &s.Name, &s.Proto, &s.PortStart, &s.PortEnd,
+		&s.Builtin, &s.Description,
+		&s.CreatedAt, &s.UpdatedAt,
+	); err != nil {
+		return nil, err
+	}
+	return &s, nil
+}