docs: fix TypeScript unrecoverable error example

[kiwigitops]

Summary

• Removes the TypeScript example that imports UnrecoverableInvocationError, which is not exported by the TypeScript SDK.
• Replaces it with the public retryStrategy: () => ({ shouldRetry: false }) pattern for non-retryable step failures.

Fixes #173.

Value

Prevents readers from copying a TypeScript example that fails to compile and points them to a supported SDK pattern instead.

Validation

• Confirmed UnrecoverableInvocationError is not exported from the TypeScript SDK index.ts on main.
• Verified the updated document no longer contains UnrecoverableInvocationError and includes the no-retry retryStrategy example.

Documentation

• Updated aws-lambda-durable-functions-power/steering/error-handling.md.

Checks not run

• Documentation-only change; no local docs build was run in this sandbox.

Limitations or follow-up

• A dedicated public TypeScript unrecoverable-error API remains tracked separately in the SDK feature request linked from the issue.

[kiwigitops]

Closing this because I opened it in error: this automation should avoid docs-only PRs.