feat(server): CreateBatch/生成器切换到 codes 库(Mint 单事务全成或全无)(#codes-lib)

Store 挂库 store(NewStore 内部构造 libcodes.Store,签名不变);
generator.go 三函数委托 libcodes,ErrDuplicate 别名同一哨兵;
Service.CreateBatch 走 libcodes.Mint(签名不变)。openMigratedSQLite
挪到共享 sqlite_helper_test.go,backfill_test.go/service_sqlite_test.go
共用。Store.CreateBatch/CreateCode/CodeExistsByHash 原样保留供
webhook.go(Task 6 改用新原语,Task 7 删除)。

server/internal/codes/backfill_test.go

@@ -2,7 +2,6 @@ package codes_test
 
 import (
 	"context"
-	"database/sql"
 	"testing"
 	"time"
 
@@ -11,22 +10,6 @@ import (
 	"github.com/wangjia/pangolin/server/internal/store"
 )
 
-func openMigratedSQLite(t *testing.T) *sql.DB {
-	t.Helper()
-	db, err := store.Open(&config.Config{Driver: "sqlite", DSN: ":memory:"})
-	if err != nil {
-		t.Fatalf("open: %v", err)
-	}
-	t.Cleanup(func() { _ = db.Close() })
-	if err := store.MigrateUp(db, "sqlite"); err != nil {
-		t.Fatalf("migrate: %v", err)
-	}
-	if err := store.ApplyCodesLibMigrations(context.Background(), db, "sqlite"); err != nil {
-		t.Fatalf("lib migrate: %v", err)
-	}
-	return db
-}
-
 func TestBackfillLegacy(t *testing.T) {
 	ctx := context.Background()
 	db := openMigratedSQLite(t)