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/styles.css

@@ -1217,6 +1217,32 @@ nav button svg { width: 14px; height: 14px; color: var(--ink-3); }
   font-family: var(--font-mono);
   letter-spacing: .02em;
 }
+/* 注册码优先:验码行(输入 + 验证按钮)+ 状态提示 + 只读团队名 */
+.auth-exact-page .invite-verify-row {
+  display: flex;
+  align-items: stretch;
+  gap: 8px;
+}
+.auth-exact-page .invite-verify-row .field-input-wrap { flex: 1; }
+.auth-exact-page .invite-verify-btn {
+  flex-shrink: 0;
+  height: auto;
+  align-self: stretch;
+  padding: 0 18px;
+  white-space: nowrap;
+}
+.auth-exact-page .field-note.ok {
+  color: var(--accent-forest);
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+}
+.auth-exact-page .field-note.err { color: var(--accent-crimson); }
+.auth-exact-page .field-input-wrap.is-readonly input {
+  background: var(--black-alpha-4);
+  color: var(--black-alpha-56);
+  cursor: default;
+}
 .auth-exact-page .agree {
   display: flex;
   align-items: flex-start;