feat: add SEND_MAIL delivery and quota controls (#986)

* feat: add SEND_MAIL delivery and quota controls

* test: cover -1 unlimited runtime for send mail quota

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix: split send limit validation and save

* refactor: move send limit counters to settings

* fix: polish send mail limit review follow-ups

* docs: note SEND_MAIL breaking change

* test: align send mail limit e2e with new messages

* fix: address review follow-ups

* fix: harden admin send mail handlers

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Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -8,8 +8,14 @@
 
 ## v1.7.0(main)
 
+### Breaking Changes
+
+- breaking: |发信| `SEND_MAIL` 的语义已从“仅用于 `verifiedAddressList` 命中的兼容发信路径”调整为“常规兜底发信通道”。如果实例已绑定 `SEND_MAIL` 且未配置 Resend/SMTP，升级后未命中 `verifiedAddressList` 的收件人也会直接通过 Cloudflare binding 发出，发信行为与成本路径会发生变化
+
 ### Features
 
+- feat: |发信| 推荐使用 Cloudflare `send_email` binding 作为默认发信通道，已 onboard Email Routing 的域名未配置 Resend/SMTP 时自动走 binding 发至任意地址（Workers Paid 每月含 3000 封，超出 $0.35/1000 封）；历史 `verifiedAddressList` / Resend / SMTP 配置完全兼容（#964）
+
 ### Bug Fixes
 
 - fix: |用户侧收件箱| 修复 `ENABLE_USER_DELETE_EMAIL` 关闭时用户中心仍显示删除按钮且仍可通过 `/user_api/mails/:id` 删除邮件的问题（#978）