Extend the fcitx5 plugin with SetQaHotkeyRaw/SetTranslationHotkeyRaw DBus methods and corresponding signals, so that QA panel toggle and translation modifier hotkeys work on Linux (not just the main dictation hotkey). Built-in Shift key translation modifier also handled by the plugin. Document DBus security model in plugin header. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>