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/en.yaml

@@ -90,6 +90,12 @@ user.wechat_id_empty: "WeChat ID is empty!"
 user.telegram_id_empty: "Telegram ID is empty!"
 user.telegram_not_bound: "This Telegram account is not bound"
 user.linux_do_id_empty: "Linux DO ID is empty!"
+user.sms_verification_required: "SMS verification is enabled, please enter your phone number and verification code"
+user.phone_format_invalid: "Invalid phone number format"
+user.phone_already_taken: "This phone number is already registered"
+user.send_sms_failed: "Failed to send SMS, please try again later"
+user.sms_not_configured: "SMS service is not configured"
+user.phone_empty: "Phone number cannot be empty"
 
 # Quota messages
 quota.negative: "Quota cannot be negative!"