Add keyboard shortcut to enter fullscreen scroll/select mode from chat

Feature request

The new fullscreen scroll layout (with auto-copy on mouse selection) is nice, but keyboard support for scroll/select is limited.

Problem

From chat input, there is no keyboard-only path to enter scroll/select mode. Mouse wheel or click-drag is required to shift focus into the Scroll context.

Even the Scroll-context bindings exposed via ~/.claude/keybindings.json (scroll:lineUp/Down, selection:extendLeft/Right, selection:copy) do not appear to fire reliably in practice — focus stays with the chat input.

Ask

• Add a bindable action to enter scroll/select mode from chat (e.g. scroll:enter / focus:scroll).
• Make the existing Scroll-context bindings actually work once focus is in the scroll view, so users can navigate and select via keyboard only (no mouse).

Env

Claude Code CLI, macOS, iTerm2 + tmux