fix(migrate): copy composite-key tables without FindInBatches (#4787)

SQLite to Postgres migration aborted with "copy *model.ClientInbound:
primary key required" on installs whose client_inbounds table exceeds
one read batch (500 rows). gorm's FindInBatches pages between batches
using a single PrioritizedPrimaryField, which composite-key tables
(client_id + inbound_id, no surrogate id) do not have, so it returns
ErrPrimaryKeyRequired once a table holds more than one batch.

Replace FindInBatches in copyTable with explicit LIMIT/OFFSET paging
ordered by the model's primary-key columns. This works for every table
including composite-key ones, keeps memory bounded, and changes no
schema.

Add a Postgres-gated regression test covering a >500-row composite-key
table.

database/migrate_data_test.go

@@ -0,0 +1,64 @@
+package database
+
+import (
+	"os"
+	"testing"
+
+	"github.com/mhsanaei/3x-ui/v3/database/model"
+
+	"gorm.io/driver/postgres"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+	"gorm.io/gorm/logger"
+)
+
+func TestMigrateData_CompositeKeyTableLargerThanBatch(t *testing.T) {
+	dsn := os.Getenv("XUI_TEST_PG_DSN")
+	if dsn == "" {
+		t.Skip("set XUI_TEST_PG_DSN to a reachable Postgres to run this test")
+	}
+
+	// Seed a SQLite source with the full schema and >500 client_inbounds rows.
+	srcPath := t.TempDir() + "/x-ui.db"
+	src, err := gorm.Open(sqlite.Open(srcPath), &gorm.Config{Logger: logger.Discard})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	for _, m := range migrationModels() {
+		if err := src.AutoMigrate(m); err != nil {
+			t.Fatalf("automigrate %T: %v", m, err)
+		}
+	}
+	const n = 600 // > batchSize (500) so the between-batches path is exercised
+	links := make([]model.ClientInbound, 0, n)
+	for i := 1; i <= n; i++ {
+		links = append(links, model.ClientInbound{ClientId: i, InboundId: 1})
+	}
+	if err := src.CreateInBatches(links, 200).Error; err != nil {
+		t.Fatalf("seed client_inbounds: %v", err)
+	}
+	if sqlDB, err := src.DB(); err == nil {
+		sqlDB.Close() // flush before MigrateData reopens the file
+	}
+
+	// Make the test re-runnable: drop any tables from a previous run.
+	dst, err := gorm.Open(postgres.Open(dsn), &gorm.Config{Logger: logger.Discard})
+	if err != nil {
+		t.Fatalf("open postgres: %v", err)
+	}
+	if err := dst.Migrator().DropTable(migrationModels()...); err != nil {
+		t.Fatalf("drop tables: %v", err)
+	}
+
+	if err := MigrateData(srcPath, dsn); err != nil {
+		t.Fatalf("MigrateData: %v", err) // fails here before the fix
+	}
+
+	var got int64
+	if err := dst.Model(&model.ClientInbound{}).Count(&got).Error; err != nil {
+		t.Fatalf("count: %v", err)
+	}
+	if got != n {
+		t.Fatalf("client_inbounds rows = %d, want %d", got, n)
+	}
+}