feat: 实现PIPL数据主体删除权支持功能

- 新增 LeadDeletionRequest 模型，支持邮箱验证的删除申请/确认流程
- POST /api/v1/custom/leads/deletion-requests/ 发起申请（通用响应避免探测邮箱是否存在）
- POST /api/v1/custom/leads/deletion-requests/confirm/ 确认删除（24小时token有效期）
- 按邮箱在 Lead.data 中匹配并删除对应记录，跨SQLite/Postgres使用Python级匹配
- LeadDeletionRequest 通过 Django Admin 只读展示供合规审计
- 新增 FRONTEND_BASE_URL 设置用于拼接邮件确认链接
- apps/forms/tests.py 新增6个测试用例（含节流缓存隔离修复），全仓库30个用例通过
- 更新设计文档 §2.15/§2.16 勾选项

apps/forms/urls.py

@@ -1,7 +1,17 @@
 from django.urls import path
 
-from .views import LeadSubmitView
+from .views import LeadDeletionConfirmView, LeadDeletionRequestView, LeadSubmitView
 
 urlpatterns = [
     path("leads/", LeadSubmitView.as_view(), name="lead-submit"),
+    path(
+        "leads/deletion-requests/",
+        LeadDeletionRequestView.as_view(),
+        name="lead-deletion-request",
+    ),
+    path(
+        "leads/deletion-requests/confirm/",
+        LeadDeletionConfirmView.as_view(),
+        name="lead-deletion-confirm",
+    ),
 ]