chore: code cleanup and documentation overhaul

- Remove debug header dump from MITM proxy (was temp debugging code)
- Suppress dead_code warnings for intentional OpenAI compat fields
- Rewrite README with styled mermaid architecture diagrams, full
  feature listing, usage examples, and CLI reference
- Update endpoint-gap-analysis: images implemented, audio only stretch
- Update mitm-interception-status: add request modification and error
  capture components
- Update standalone-ls-todo: add new endpoints to test results
- Zero compiler warnings

src/mitm/proxy.rs

@@ -633,16 +633,6 @@ async fn handle_http_over_tls(
         };
 
         // Forward the request — if write fails, reconnect and retry once
-        // DEBUG: dump headers and total size
-        if req_path.contains("streamGenerateContent") {
-            let hdr_end = find_headers_end(&request_buf).unwrap_or(request_buf.len());
-            let hdr_str = String::from_utf8_lossy(&request_buf[..hdr_end.min(request_buf.len())]);
-            info!(
-                total_buf_len = request_buf.len(),
-                body_len = request_buf.len() - hdr_end,
-                "MITM: sending request to upstream\n{hdr_str}"
-            );
-        }
         if let Err(e) = conn.write_all(&request_buf).await {
             debug!(domain, error = %e, "MITM: upstream write failed, reconnecting");
             let c = connect_upstream(domain, &upstream_config).await?;