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/backend/apps/accounts/views.py

@@ -83,6 +83,34 @@ def register(request):
     return Response(auth_payload(data["user"], data["team"], token), status=status.HTTP_201_CREATED)
 
 
+@api_view(["POST"])
+@permission_classes([])
+def validate_invite(request):
+    """免登录验码:注册页「填码 → 验过才展开表单」用。
+    返回 {valid, kind, team_name?, role?};无效返回 {valid:false, detail}(始终 200,不暴露是否存在以外的细节)。"""
+    from django.utils import timezone
+
+    code = str(request.data.get("code") or request.data.get("invite_code") or "").strip().upper()
+    if not code:
+        return Response({"valid": False, "detail": "请填写邀请码"})
+    inv = Invitation.objects.select_related("team").filter(code=code).first()
+    if inv is None:
+        return Response({"valid": False, "detail": "邀请码不存在"})
+    if inv.status != Invitation.Status.PENDING:
+        return Response({"valid": False, "detail": "邀请码已被使用或已撤销"})
+    if inv.expires_at <= timezone.now():
+        return Response({"valid": False, "detail": "邀请码已过期"})
+    return Response(
+        {
+            "valid": True,
+            "kind": inv.kind,
+            "role": inv.role,
+            # join_team 回团队名(只读展示);create_team 无团队
+            "team_name": inv.team.name if inv.team_id else None,
+        }
+    )
+
+
 @api_view(["POST"])
 @permission_classes([])
 def login(request):
@@ -265,6 +293,7 @@ def team_invitations(request):
         role = TeamMember.Role.ADMIN  # 邀请不允许 OWNER(Team.owner 唯一)
     invite = Invitation.objects.create(
         team=team,
+        kind=Invitation.Kind.JOIN_TEAM,  # 团管发的码恒为「加入本团队」
         role=role,
         email=str(request.data.get("email") or "").strip(),
         monthly_credit_limit=request.data.get("monthly_credit_limit") or request.data.get("monthly") or 0,