Timeline command components crash on unexpected payload shapes

Several timeline command components assume specific payload shapes and will throw if the data doesn't match. An error boundary was added in #1598 to prevent these from crashing the app, but the components themselves should add defensive guards.

Vulnerable components:

• AsyncStorageMutationCommand — payload.data.key accessed without null check
• ApiResponseCommand — payload.request and payload.response destructured without null checks
• StateValuesChangeCommand — insufficient type checking before Object.keys()
• BenchmarkReportCommand — payload.steps array accessed without validation, crashes on empty array
• SagaTaskCompleteCommand/Stateless — payload.children.length and .map() without array check

These were safe when the only payload source was the client SDK, but with the MCP server (#1598) there's now a second source of commands that may produce different shapes.