When soft-wrapping text, `LineWrapper::is_word_char` determines which
characters stick to the preceding word at wrap boundaries. The list
already includes trailing punctuation like `,`, `.`, and `:`, but was
missing `;`. As a result, a message like "we won't pass it on; no big
deal" could wrap with `;` isolated at the start of the next line (`on` /
`; no`).

This was most visible in the agent panel message editor but affects any
surface that uses soft-wrapping.

Also adds `assert_word("on;")` to `test_is_word_char` to guard against
regressions.

Release Notes:

- Fixed trailing `;` being wrapped to a new line instead of staying
attached to the preceding word.