remove Anthropic backend, add request logging on timeout

Delete anthropic.rs (713 lines) — we only use OpenAI-compatible
endpoints (vLLM, OpenRouter). Simplify ApiClient to store base_url
directly instead of Backend enum.

SseReader now stores the serialized request payload and saves it
to ~/.consciousness/logs/failed-request-{ts}.json on stream timeout,
so failed requests can be replayed with curl for debugging.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/api/openai.rs

@@ -68,6 +68,7 @@ pub async fn stream_events(
     .await?;
 
     let mut reader = super::SseReader::new(ui_tx);
+    reader.set_request(&request);
 
     let mut content_len: usize = 0;
     let mut reasoning_chars: usize = 0;