feat(admin): Phase 1 注册邀请码逻辑 — 码必填 + kind 分流 + validate-invite + 注册页码优先重做

后端:Invitation.kind(join_team/create_team)+ team 可空 + migration;RegisterSerializer 邀请码必填,
create_team 开新团队当 owner+发试用额度、join_team 幂等入伙不重复发额度,删「空码开团队」;
validate-invite 免登录验码端点;团管发码恒 join_team;InvitationSerializer 增 kind/team_name。
前端:注册页码优先(验过才展开;create_team 填团队名 / join_team 只读团队名,不暴露团队列表)、
邀请链接 ?invite= 自动验码、api.validateInvite、验码行/状态提示样式(仅 token)。
测试:accounts 22/22 单测过(RegisterInviteCodeTests + ValidateInviteTests);
无头 e2e _admin-p1.mjs 全断言过 + 0 console error;tsc+build 绿。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

core/frontend/src/api.ts

@@ -106,9 +106,16 @@ async function request<T>(path: string, options: RequestInit = {}): Promise<T> {
 }
 
 export const api = {
-  register(payload: { username: string; password: string; email?: string; team_name?: string; invite_code?: string }) {
+  register(payload: { username: string; password: string; email?: string; team_name?: string; invite_code: string }) {
     return request<AuthPayload>("/api/auth/register/", { method: "POST", body: JSON.stringify(payload) });
   },
+  // 免登录验码:注册页「填码 → 验过才展开表单」。始终 200,以 valid 标志区分。
+  validateInvite(code: string) {
+    return request<{ valid: boolean; kind?: "join_team" | "create_team"; role?: string; team_name?: string | null; detail?: string }>(
+      "/api/auth/validate-invite/",
+      { method: "POST", body: JSON.stringify({ code }) }
+    );
+  },
   login(payload: { username: string; password: string }) {
     return request<AuthPayload>("/api/auth/login/", { method: "POST", body: JSON.stringify(payload) });
   },