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/store.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 	"time"
 
+	libcodes "github.com/wangjia/codes"
 	dbx "github.com/wangjia/pangolin/server/internal/db"
 )
 
@@ -80,10 +81,21 @@ type BatchRow struct {
 type Store struct {
 	db      *sql.DB
 	dialect dbx.Dialect
+	lib     *libcodes.Store
 }
 
 // NewStore creates a Store backed by the given connection pool (MySQL or SQLite).
-func NewStore(db *sql.DB) *Store { return &Store{db: db, dialect: dbx.DialectForDB(db)} }
+func NewStore(db *sql.DB) *Store {
+	d := dbx.DialectForDB(db)
+	libD := libcodes.DialectMySQL
+	if d.Name() == "sqlite" {
+		libD = libcodes.DialectSQLite
+	}
+	return &Store{db: db, dialect: d, lib: libcodes.NewStore(db, libD)}
+}
+
+// Lib exposes the shared library store (used by Service / webhook shim).
+func (s *Store) Lib() *libcodes.Store { return s.lib }
 
 // --------------------------------------------------------------------------
 // Batch and code creation (used by Service.CreateBatch and webhook)