Feature request: adjustable line/column width in desktop app

Currently the chat/conversation column in the Claude desktop app is a fixed, centered width, which wraps text well before the edge of the window on wide monitors. There are existing requests to either widen it (#57991) or cap it for readability (#63813), which pull in opposite directions. Rather than picking one fixed width, it would be great if the line/column width were user-adjustable (e.g. a slider or setting in Preferences), so people can set it to their own preference regardless of screen size.

Related: #57991, #63813, #57749