serve: a tool call inside a code fence or inline code in the visible answer is text (#1058)

The live smoke showed the same quoted-example problem in the answer: a model that wrote the call format in a
fenced example after </think> got a real tool call. The content parser now uses the fence / inline-code
tracking of the reasoning rescue: an opener inside a ``` or ~~~ fence (tracked across stream chunks) or inside
inline code stays text, the decision depending only on the text before it, so streamed and whole outputs agree.
Openers at the top level fire as before, including one after a sentence on the same line (none of the 37
corpus specimens needed that, but the old tests do and nothing argues against it). A closed call at the end of
an answer cut by max tokens stays a call.

Tests: quoted calls stay text and real ones fire at every chunk split; OpenAI (whole and streamed), Anthropic
and Responses over HTTP.