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/error.rs

@@ -60,6 +60,9 @@ pub enum ApiError {
         retryable: bool,
         /// Suggested user action based on error type (e.g., "Reduce prompt size" for 413)
         suggested_action: Option<String>,
+        /// Parsed Retry-After header value (seconds) for 429 responses.
+        /// When present, overrides the exponential backoff delay.
+        retry_after: Option<Duration>,
     },
     RetriesExhausted {
         attempts: u32,
@@ -128,6 +131,18 @@ impl ApiError {
     }
 
     #[must_use]
+    /// Return the `Retry-After` delay if this error came from a 429 response
+    /// that included a `retry-after` header. Callers should prefer this value
+    /// over the computed backoff delay when it exists.
+    #[must_use]
+    pub fn retry_after(&self) -> Option<Duration> {
+        match self {
+            Self::Api { retry_after, .. } => *retry_after,
+            Self::RetriesExhausted { last_error, .. } => last_error.retry_after(),
+            _ => None,
+        }
+    }
+
     pub fn is_retryable(&self) -> bool {
         match self {
             Self::Http(error) => error.is_connect() || error.is_timeout() || error.is_request(),
@@ -499,6 +514,7 @@ mod tests {
             body: String::new(),
             retryable: true,
             suggested_action: None,
+        retry_after: None,
         };
 
         assert!(error.is_generic_fatal_wrapper());
@@ -522,6 +538,7 @@ mod tests {
                 body: String::new(),
                 retryable: true,
                 suggested_action: None,
+            retry_after: None,
             }),
         };
 
@@ -543,6 +560,7 @@ mod tests {
             body: String::new(),
             retryable: false,
             suggested_action: None,
+        retry_after: None,
         };
 
         assert!(error.is_context_window_failure());