test(llm): the response cap is pinned at its boundary and as the production default (#53)

Only the 8-byte override was exercised; >= vs >, a huge default and a non-positive option
all stayed green. Also says why the error-body read ignores its error. Found by the PR #58
review.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/adapters/llm/client.go

@@ -202,6 +202,7 @@ func (c *Client) Complete(ctx context.Context, system, user string) (string, err
 
 	if resp.StatusCode != http.StatusOK {
 		// Only the bounded head is ever used (HTTPError.Error truncates to it), so read no more.
+		// A read error here only shortens a diagnostic; the status code below is what callers act on.
 		head, _ := io.ReadAll(io.LimitReader(resp.Body, maxErrorBody+1))
 		return "", &HTTPError{Code: resp.StatusCode, Body: string(head)}
 	}