feat: API timeout config, Retry-After header, configurable retry, and 400 transient retry

Cherry-picked from PR #2816 onto current upstream/main, resolving
conflicts from PR #3015's merge (which added retry_after to ApiError
but some construction sites were missing it).

Commits preserved:
- ade85398: API timeout config, Retry-After header, configurable retry
  - TimeoutConfig in HTTP client builder (connect 30s, request 5min)
  - CLAW_API_CONNECT_TIMEOUT and CLAW_API_REQUEST_TIMEOUT env vars
  - Retry-After header parsing on 429 responses
  - ApiTimeoutConfig in runtime config (settings.json)
- 8a883430: retry 400 responses with transient gateway error bodies
  - Detects known gateway phrases in 400 response bodies
  - Marks them as retryable instead of hard-failing
- ed91a61e: add 'no parseable body' to CONTEXT_WINDOW_ERROR_MARKERS
  - Some providers return 400 with 'no parseable body' for oversized
    requests instead of a proper context_length_exceeded error

Commits skipped (already in upstream via PR #3015):
- 453ab642: optional id field (already merged)
- baa8d1ba: HTML detection in streaming (already merged)
- 33d2f789: JSON error detection in streaming (already merged)

8 files changed, 299 insertions, 80 deletions

rust/crates/api/src/providers/openai_compat.rs

@@ -1667,7 +1667,10 @@ async fn expect_success(response: reqwest::Response) -> Result<reqwest::Response
     })
 }
 
-fn parse_retry_after(headers: &reqwest::header::HeaderMap, status: reqwest::StatusCode) -> Option<std::time::Duration> {
+fn parse_retry_after(
+    headers: &reqwest::header::HeaderMap,
+    status: reqwest::StatusCode,
+) -> Option<std::time::Duration> {
     if status != reqwest::StatusCode::TOO_MANY_REQUESTS {
         return None;
     }