fix(user): assign snowflake IDs on registration

The HTTP register path left ID at 0, so SQLite/GORM filled a
serial primary key. CreateUser now generates a snowflake ID when
none is set, matching admin create and OAuth signup.

backend/plugins/domain/user/plugin_test.go

@@ -166,6 +166,8 @@ func TestUserLoginHTTPHandler(t *testing.T) {
 		IsActive: true,
 	}
 	require.NoError(t, user.CreateUser(context.Background(), plainUser))
+	require.NotZero(t, plainUser.ID)
+	require.Greater(t, plainUser.ID, uint64(10000), "user id must be snowflake, not sqlite autoincrement")
 
 	reqBodyPlain := `{"username":"plain_admin","password":"12345678"}`
 	reqPlain, _ := http.NewRequest(http.MethodPost, "/api/v1/user/login", bytes.NewBufferString(reqBodyPlain))

backend/plugins/domain/user/repository.go

@@ -6,6 +6,7 @@ package user
 import (
 	"Wavelet/core"
 	"Wavelet/core/contracts"
+	"Wavelet/pkg/idgen"
 	"Wavelet/pkg/util"
 	"context"
 	"errors"
@@ -82,8 +83,11 @@ func GetUserByEmail(ctx context.Context, email string) (*User, error) {
 	return &u, nil
 }
 
-// CreateUser 创建用户
+// CreateUser 创建用户。ID 为空时用雪花算法分配，避免 SQLite/GORM 把 0 当成自增主键。
 func CreateUser(ctx context.Context, u *User) error {
+	if u != nil && u.ID == 0 {
+		u.ID = idgen.NextUint64ID()
+	}
 	return getDB(ctx).Create(u).Error
 }