feat: introduce i18n system and class invitation codes

Add complete i18n infrastructure using next-intl (cookie-driven, without i18n routing) with zh-CN/en dictionary files, locale switcher, and NextIntlClientProvider in root layout. Add class invitation code system with new class_invitation_codes table, data-access layer (generate/validate/consume/revoke), server actions with permission checks, rate limiting, and audit logging. Add class-invitation-manager UI component. Refactor onboarding stepper to use i18n translations and accept new invitation code format (6-char alphanumeric) with backward compatibility for legacy 6-digit codes.

src/modules/classes/data-access.ts

@@ -613,22 +613,26 @@ export async function enrollStudentByInvitationCode(studentId: string, invitatio
   const sid = studentId.trim()
   const code = invitationCode.trim()
   if (!sid) throw new Error("Missing student id")
-  if (!/^\d{6}$/.test(code)) throw new Error("Invalid invitation code")
+  if (!code) throw new Error("Invalid invitation code")
 
-  const [cls] = await db
-    .select({ id: classes.id })
-    .from(classes)
-    .where(eq(classes.invitationCode, code))
-    .limit(1)
-
-  if (!cls) throw new Error("Invalid invitation code")
+  // v3：优先走新邀请码体系（validateInvitationCode 内部含 fallback 到旧 classes.invitationCode）
+  const { validateInvitationCode, consumeInvitationCode } = await import("./data-access-invitations")
+  const result = await validateInvitationCode(code)
+  if (!result.valid || !result.classId) {
+    throw new Error("Invalid invitation code")
+  }
 
   await db
     .insert(classEnrollments)
-    .values({ classId: cls.id, studentId: sid, status: "active" })
+    .values({ classId: result.classId, studentId: sid, status: "active" })
     .onDuplicateKeyUpdate({ set: { status: "active" } })
 
-  return cls.id
+  // 消耗新表邀请码（旧表无计数，跳过）
+  if (result.codeId) {
+    await consumeInvitationCode(code)
+  }
+
+  return result.classId
 }
 
 export async function enrollTeacherByInvitationCode(
@@ -639,7 +643,7 @@ export async function enrollTeacherByInvitationCode(
   const tid = teacherId.trim()
   const code = invitationCode.trim()
   if (!tid) throw new Error("Missing teacher id")
-  if (!/^\d{6}$/.test(code)) throw new Error("Invalid invitation code")
+  if (!code) throw new Error("Invalid invitation code")
 
   const [teacher] = await db
     .select({ id: users.id })
@@ -651,10 +655,17 @@ export async function enrollTeacherByInvitationCode(
 
   if (!teacher) throw new Error("Teacher not found")
 
+  // v3：优先走新邀请码体系（validateInvitationCode 内部含 fallback 到旧 classes.invitationCode）
+  const { validateInvitationCode, consumeInvitationCode } = await import("./data-access-invitations")
+  const result = await validateInvitationCode(code)
+  if (!result.valid || !result.classId) {
+    throw new Error("Invalid invitation code")
+  }
+
   const [cls] = await db
     .select({ id: classes.id, teacherId: classes.teacherId })
     .from(classes)
-    .where(eq(classes.invitationCode, code))
+    .where(eq(classes.id, result.classId))
     .limit(1)
 
   if (!cls) throw new Error("Invalid invitation code")
@@ -747,6 +758,11 @@ export async function enrollTeacherByInvitationCode(
     if (!assigned) throw new Error("Class already has assigned teachers")
   }
 
+  // 消耗新表邀请码（旧表无计数，跳过）
+  if (result.codeId) {
+    await consumeInvitationCode(code)
+  }
+
   return cls.id
 }