[FEATURE]: Add tui.json option to set sidebar hidden by default

[dwen3232]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Currently, the TUI sidebar (right panel) can be toggled at runtime via the sidebar_toggle keybind (<leader>b by default), but there is no way to configure it to be hidden by default on startup.

Request: Add a tui.json config option to control the sidebar's initial visibility state, for example:

{
  "$schema": "https://opencode.ai/tui.json",
  "sidebar": {
    "visible": false
  }
}

Benefits:

• Users who prefer a minimal, full-width chat layout can set this once and not have to toggle it every session.
• The sidebar takes up significant horizontal space, which is especially noticeable on smaller terminal windows or when using a split-pane tmux setup.
• The toggle keybind already exists, so the underlying mechanism is in place — this just needs a way to set the initial state via config.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Add a config to set the sidebar to open/closed by default #3682: [FEATURE]: Add a config to set the sidebar to open/closed by default — same request to configure the sidebar's default open/closed state via a config option.

Since this issue mentions keybinds, please also check our pinned keybinds documentation: #4997