Failure markers now carry finish_reason and usage tokens (prompt /
completion / reasoning) pulled from the chat-completions response, so
the case-page "Technische Details" block can show why an analysis
truncated — e.g. gpt-oss-120b hitting max_completion_tokens with the
chain-of-thought before producing any visible answer.
The worker also emits a new CaseEventKind::AnalysisFailed after writing
the marker, so subscribed browsers reload immediately instead of leaving
the page on the "Wird analysiert …" placeholder.
