Add option to strip/disable left gutter so copied multi-line output has no leading spaces

Problem

Assistant messages are rendered with a fixed left gutter (the ⏺ marker on the first line and a matching indent on continuation lines). When selecting multi-line output with the mouse to copy it, every line after the first carries the gutter's leading space(s). Pasting elsewhere yields text with unwanted leading whitespace on each line.

Impact

Copy-pasting any multi-line assistant output (prose, commands, snippets rendered outside a code fence) requires manual cleanup or fiddly terminal rectangular-selection gymnastics that conflict with common terminal settings (e.g. iTerm2's "⌥-Click moves cursor" prevents ⌥+drag block selection).

Requested

Any one of:

1. A setting to disable/reduce the left gutter for assistant messages.
2. A "copy message" affordance (keybinding or command) that yields gutter-free text.
3. Strip the gutter indentation automatically from OSC 52 / clipboard copy paths.

Environment

• Claude Code CLI on macOS (Darwin), iTerm2
• Terminal mouse selection includes the rendered left margin