Refs #2215 Fix B: remove the mid-response stripping hazard without losing leading multi-line wrapper cleanup.
The pattern now strips only a leading 'the user is asking' wrapper line and preserves the visible answer that follows. Add regression coverage for both the leading-wrapper and mid-response prose cases.
Fixes <|turn|>thinking delimiter (was wrong as <|turn>thinking) in api/streaming.py, static/messages.js, and static/ui.js. Adds 13 regression tests. Independent review by @nesquena.