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/generator.go

@@ -8,16 +8,14 @@
 package codes
 
 import (
-	"errors"
-
-	"github.com/wangjia/pangolin/server/internal/idgen"
+	libcodes "github.com/wangjia/codes"
 )
 
 // GenerateCode generates a single random activation code in canonical Crockford
 // Base32 form (15 random data chars + 1 check char = 16 chars total).
-// It delegates to idgen.GenerateCode which uses crypto/rand.
+// It delegates to the shared library, which uses crypto/rand.
 func GenerateCode() (string, error) {
-	return idgen.GenerateCode()
+	return libcodes.GenerateCode()
 }
 
 // Canonicalize converts an activation-code string into canonical form:
@@ -27,15 +25,17 @@ func GenerateCode() (string, error) {
 // Crockford alphabet, if the length is not exactly 16, or if the check character
 // is incorrect.
 func Canonicalize(code string) (string, error) {
-	return idgen.CanonicalizeCode(code)
+	return libcodes.Canonicalize(code)
 }
 
 // Hash returns the hex-encoded SHA-256 of the canonical plaintext code.
 // This is the value stored in the database; the plaintext is never stored.
 func Hash(canonical string) string {
-	return idgen.HashCode(canonical)
+	return libcodes.Hash(canonical)
 }
 
 // ErrDuplicate is returned by the batch generator when a generated code
 // already exists in the database (hash collision).  The caller should retry.
-var ErrDuplicate = errors.New("codes: duplicate code hash")
+// Aliased to the same sentinel as the shared library so errors.Is succeeds
+// across both layers.
+var ErrDuplicate = libcodes.ErrDuplicate