settings: complete remaining i18n in Account and Preferences sections

[tyreseluo]

Summary

• complete i18n wiring for Settings -> Preferences -> App
  • localize section labels, dropdown options, helper text, popup messages, and thumbnail option labels
  • ensure Current setting: ... shortcut description updates correctly after language switch
• complete i18n wiring for Settings -> Account verification banner
  • localize verified/unverified banner copy
  • localize unverified hint text and device/session info formatting
  • localize unsupported-avatar-delete warning
• pass app_language through SettingsScreen -> AppSettings::populate to keep runtime strings in sync

Files Changed

• src/settings/app_settings.rs
• src/settings/account_settings.rs
• src/settings/settings_screen.rs
• resources/i18n/en.json
• resources/i18n/zh-CN.json

Validation

• cargo build -q passed

Notes

• scope is intentionally limited to settings-page i18n completion in this PR.