feat: add SMS verification registration with UniSMS provider

- Add phone field to user model with index and helper methods
- Implement SMS provider interface with UniSMS (合一短信) implementation
- Add SMS verification code sending endpoint with rate limiting (1/60s)
- Support SMS registration in Register() (mutually exclusive with email)
- Add SMS configuration to admin settings (provider, keys, signature, template)
- Display phone number in admin user list contact column
- Add i18n translations for all SMS-related messages (zh-CN, en, zh-TW)
- Add Claude Code skills: sync-upstream, migrate-server
- Update CLAUDE.md with git conventions and deployment guide

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

i18n/locales/zh-TW.yaml

@@ -91,6 +91,12 @@ user.wechat_id_empty: "WeChat id 為空！"
 user.telegram_id_empty: "Telegram id 為空！"
 user.telegram_not_bound: "該 Telegram 帳號未綁定"
 user.linux_do_id_empty: "Linux DO id 為空！"
+user.sms_verification_required: "管理員開啟了簡訊驗證，請輸入手機號和驗證碼"
+user.phone_format_invalid: "手機號格式不正確"
+user.phone_already_taken: "該手機號已被註冊"
+user.send_sms_failed: "簡訊發送失敗，請稍後重試"
+user.sms_not_configured: "簡訊服務未配置"
+user.phone_empty: "手機號不能為空"
 
 # Quota messages
 quota.negative: "額度不能為負數！"