v0.1.21

Fix opaque "Gemini/Claude API request failed" errors

Both call_anthropic() and call_gemini() were still on the original
curl -sf ... || fail "<generic message>" form from before the exit-code/
HTTP-body capturing pattern existed (built out for call_ollama() and
call_openai() since). A real API-level failure - bad model name, quota
exceeded, bad key - came through as a bare "Gemini API request failed" or
"Claude API request failed" with zero indication of what actually went
wrong, which is exactly what was just reported.

Both now match the other two providers: distinguish curl exit code (host
unreachable) from an HTTP error status with the actual error.message body
surfaced directly. Verified against mocked 400/429 responses - both now
report the real cause instead of the generic message.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>