Fix 'workflow not found' when the chat assistant creates a workflow

[Evanfeenstra]

What changed

ChatFlyout now calls onWorkflowCreated from onToolResult instead of onToolCall. It only fires when create_workflow succeeds (output.ok), and it passes the name the server returns (output.name).

Why

When the assistant created a workflow, the UI showed "workflow not found" until the page was refreshed. The tool-input event fires before the tool runs, so the sidebar refresh and getWorkflowFlow fetch happened before the workflow existed and got a 404. That set loadError.

This also fixes two related problems:

• Renamed workflows: if the requested name is taken, create_workflow may save under a different one, and the old code selected the requested name.
• Failed validation: when validation fails nothing is saved, but the old code still selected the workflow.

Reviewer notes

• This follows the same pattern run_workflow already uses in the same handler.
• Not typechecked or tested in the running app. The worktree had no node_modules.
• To check it: ask the assistant to create a workflow. The canvas should open it with no error.