Mark subagent sessions as agent-initiated to exclude them from quota limits

Improvements

• CoreAdd chat.headers hook and update codex and copilot plugins to use it (thanks to @ananas-viber for catching)
• TerminalAdd Gruvbox theme to Web and App@swolg
• DesktopAdd Traditional Chinese language support and rename Chinese to Chinese (Simplified)@alexyaroshuk
• DesktopAdd Russian language support@alexyaroshuk
• DesktopPolish translations in app@neriousy