Documentation renders extra whitespace in verbatim blocks

[xaviershay]

Describe and demonstrate the bug

The following documentation:

README =  {{ docVerbatim (Paragraph (fill 3 (Word "X\n"))}}

Renders with an extra whitespace on lines that aren't the first.

Screenshots

Environment (please complete the following information):

> ucm --version
unison version: 3379c03 (built on 2025-07-24)
> uname -a
Linux apollo 6.1.0-29-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.123-1 (2025-01-02) x86_64 GNU/Linux

Additional context

Have also seen similar printing multiline strings when evaluating functions (that's how I got here), but haven't been able to figure out consistent repro, it seems there are some heuristics in multiline string printing that I haven't figured out.

[xaviershay]

(as a workaround, I've added a leading space so that at least alignment isn't broken)

[xaviershay]

I think I have narrowed down the bug further. Words being joined by spaces actually makes sense. A more correct way to express the original example is:

README =  {{ docVerbatim (Word "X\nX\nX"))}}

New diagnosis: multiline strings where the last line begins with whitespace, have their whitespace collapsed when rendered. For example:

```
"X X\n "
```

Adding an extra character restores whitespace:

```
"X X\n X"
```

[xaviershay]

hrmm, copy+pasting the API response and rendering it in UI Core storybook, it renders correctly.