The llmmock Anthropic stream wrote each chunk as `data:` only, so
Anthropic clients never saw the named SSE events they dispatch on and
Claude responses arrived empty even though the stream completed with
HTTP 200.
Update `sendAnthropicStream()` to emit `event: <type>` and `data:
<json>` for each Anthropic chunk while leaving the OpenAI-style streams
unchanged.
Ethan
f7aa46c4ba