feat(admin): Phase 0 平台超管基础 — is_platform_admin + IsPlatformAdmin + create_platform_admin(admin/admin123) + AdminAuditLog + Admin 后台外壳与路由 gating

后端:User.is_platform_admin + migration;权限类 IsPlatformAdmin;管理命令建 admin/admin123(幂等);
AdminAuditLog 模型 + log_admin_action() helper;me/login 对无团队超管优雅返回 team=null;UserSerializer 暴露标志。
前端:routes/admin 后台外壳(分组侧栏 + 概览 + 占位)、/admin 路由解析与 gating(超管直落、非超管纠回)、
侧栏平台入口、admin-page.css(仅 token)、IconKitSvg 补图标。
测试:accounts 11/11 单测过;无头 e2e _admin-p0.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/audit.py

@@ -0,0 +1,42 @@
+"""平台超管审计写入 helper。失败绝不阻断主流程(审计是旁路)。"""
+
+
+def _client_ip(request):
+    if request is None:
+        return None
+    forwarded = request.META.get("HTTP_X_FORWARDED_FOR", "")
+    if forwarded:
+        return forwarded.split(",")[0].strip()
+    return request.META.get("REMOTE_ADDR") or None
+
+
+def log_admin_action(
+    request,
+    action,
+    *,
+    target_type="",
+    target_id="",
+    target_name="",
+    before=None,
+    after=None,
+):
+    """记录一条平台超管操作审计。action 用动词短语(如 'invite.issue' / 'team.disable')。
+    operator_name 取当前登录用户名快照。任何异常吞掉,不影响业务返回。"""
+    from .models import AdminAuditLog
+
+    try:
+        user = getattr(request, "user", None)
+        operator = user if (user is not None and getattr(user, "is_authenticated", False)) else None
+        AdminAuditLog.objects.create(
+            operator=operator,
+            operator_name=(getattr(operator, "username", "") or ""),
+            action=action,
+            target_type=target_type or "",
+            target_id=str(target_id or ""),
+            target_name=target_name or "",
+            before=before,
+            after=after,
+            ip_address=_client_ip(request),
+        )
+    except Exception:  # noqa: BLE001 — 审计失败不应阻断主流程
+        pass