Allow option to expand width of chat conversation to full width instead of a ...

Allow option to expand width of chat conversation to full width instead of a centered column with excess whitespace on either side

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| Field | Value |
| --- | --- |
| App version | 1.0.25 |
| OS | macOS 26.4.1 |
| Theme | Fox |
| Path | /chat |
| Tenure | Day 1 |

Start at the /chat path and inspect how the conversation column width is defined and how existing display options are exposed. Done means the chat can be switched from the centered column to full width, with the option working in the macOS app and the excess side whitespace removed when enabled.

索引モデルが issue の本文から書いたものです。