feat(workspace): app mode renders the workflow as an input/output form

Adds a third workspace mode alongside create/execute: the canvas is
covered (kept mounted so ABI registrations and SSE output application
keep working) by a form view derived from the exporter's level-0 data
nodes (inputs) and leaf outputs (results), with run/cancel wired to the
existing whole-workflow execution path and step progress driven by the
node execution status store.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>