The `end` branch of _QWEN_BARE_MARKER_RE had both pipes optional
(`\|?end\|?`), so it also matched a bare `end` between whitespace and
replaced it with a space. Messages containing Ruby, Lua or shell code that
closes a block with a lone `end` had those lines deleted, and ordinary prose
lost the word too.
Require at least one pipe so only real turn markers match; `|end`, `end|`,
`|end|` and `/|end|` strip exactly as before. Applied to the duplicated
pattern in static/js/chatRenderer.js as well.
Fixes#5547
