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/runtime/src/lib.rs

@@ -65,12 +65,13 @@ pub use compact::{
     get_compact_continuation_message, should_compact, CompactionConfig, CompactionResult,
 };
 pub use config::{
-    suppress_config_warnings_for_json_mode, ConfigEntry, ConfigError, ConfigLoader, ConfigSource,
+    ApiTimeoutConfig, ConfigEntry, ConfigError, ConfigLoader, ConfigSource,
     McpConfigCollection, McpManagedProxyServerConfig, McpOAuthConfig, McpRemoteServerConfig,
     McpSdkServerConfig, McpServerConfig, McpStdioServerConfig, McpTransport,
     McpWebSocketServerConfig, OAuthConfig, ProviderFallbackConfig, ResolvedPermissionMode,
     RuntimeConfig, RuntimeFeatureConfig, RuntimeHookConfig, RuntimePermissionRuleConfig,
-    RuntimePluginConfig, ScopedMcpServerConfig, CLAW_SETTINGS_SCHEMA_NAME,
+    RuntimePluginConfig, ScopedMcpServerConfig, suppress_config_warnings_for_json_mode,
+    CLAW_SETTINGS_SCHEMA_NAME,
 };
 pub use config_validate::{
     check_unsupported_format, format_diagnostics, validate_config_file, ConfigDiagnostic,