feat: add maxDelayMs setting to cap server-requested retry delays

When a provider (e.g., Google Gemini CLI) requests a retry delay longer
than maxDelayMs (default: 60s), the request fails immediately with an
informative error instead of waiting silently for hours.

The error is then handled by agent-level auto-retry, which shows the
delay to the user and allows aborting with Escape.

- Add maxRetryDelayMs to StreamOptions (packages/ai)
- Add maxRetryDelayMs to AgentOptions (packages/agent)
- Add retry.maxDelayMs to settings (packages/coding-agent)
- Update _isRetryableError to match 'retry delay' errors

fixes #1123

packages/coding-agent/src/core/sdk.ts

@@ -295,6 +295,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 		steeringMode: settingsManager.getSteeringMode(),
 		followUpMode: settingsManager.getFollowUpMode(),
 		thinkingBudgets: settingsManager.getThinkingBudgets(),
+		maxRetryDelayMs: settingsManager.getRetrySettings().maxDelayMs,
 		getApiKey: async (provider) => {
 			// Use the provider argument from the in-flight request;
 			// agent.state.model may already be switched mid-turn.