refactor(firewall): simplify SQL queries for firewall client retrieval

Refactored the SQL queries in the Postgres repository for listing and retrieving firewall clients by introducing a constant for the selected columns. This change improves code readability and maintainability by reducing duplication in the query definitions. No functional changes were made to the data retrieval process.

internal/repository/postgres_firewall_test.go

@@ -0,0 +1,52 @@
+package repository
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"evobgp/internal/authkey"
+	"evobgp/internal/db"
+	"evobgp/internal/store"
+)
+
+func TestPostgresFirewallClientCreateAndGetIntegration(t *testing.T) {
+	dsn := os.Getenv("EVOBGP_TEST_DATABASE_URL")
+	if dsn == "" {
+		t.Skip("EVOBGP_TEST_DATABASE_URL not set")
+	}
+	ctx := context.Background()
+	pool, err := db.OpenPostgresPool(ctx, dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer pool.Close()
+	pg, err := NewPostgres(ctx, pool, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tenant, _, _, _, _ := pg.DemoIDs()
+	if tenant == "" {
+		t.Fatal("demo tenant required")
+	}
+	tok := "evobgp_fw_pgtest_" + t.Name()
+	hash := authkey.HashToken(tok)
+	client, err := pg.CreateFirewallClient(tenant, &store.FirewallClientCreate{
+		Name:          "pg-firewall-test",
+		Hostname:      "test.local",
+		TokenPrefix:   tok[:12],
+		TokenHash:     hash,
+		ClientVersion: "test/1",
+	})
+	if err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	got, err := pg.GetFirewallClient(tenant, client.ID)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	if got.Name != "pg-firewall-test" || got.Status != "pending" {
+		t.Fatalf("got %+v", got)
+	}
+	_ = pg.DeleteFirewallClient(tenant, client.ID)
+}