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

- Add TimeoutConfig to HTTP client builder with connect_timeout (30s)
  and request_timeout (5min) defaults, configurable via
  CLAW_API_CONNECT_TIMEOUT and CLAW_API_REQUEST_TIMEOUT env vars
- Add with_timeout() builder to both AnthropicClient and
  OpenAiCompatClient for per-client timeout configuration
- Parse Retry-After header on 429 responses and use it to override
  exponential backoff delay when present
- Add ApiTimeoutConfig to runtime config with apiTimeout settings
  in ~/.claw/settings.json (connectTimeout, requestTimeout, maxRetries)
- Add retry_after field to ApiError::Api for propagating rate limit
  backoff hints through the retry pipeline

rust/crates/api/src/lib.rs

@@ -12,7 +12,9 @@ pub use client::{
 };
 pub use error::ApiError;
 pub use http_client::{
-    build_http_client, build_http_client_or_default, build_http_client_with, ProxyConfig,
+    TimeoutConfig,
+    build_http_client, build_http_client_or_default, build_http_client_with,
+    build_http_client_with_opts, ProxyConfig,
 };
 pub use prompt_cache::{
     CacheBreakEvent, PromptCache, PromptCacheConfig, PromptCachePaths, PromptCacheRecord,