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.
Remove ^ anchor from think/Gemma regexes in ui.js; trimStart() before startsWith checks in messages.js streaming path. Fixes MiniMax M2.7 and any model emitting leading newlines before <think>. 10 new tests, 768 total.