feat(platform): one command runs the workshop locally on port 4310

npm start builds the interface, refuses a busy port and names its owner, warns when OpenCode is not reachable, and prints one URL. The default port moves from 4200 (held by unrelated software on this host) to 4310. Sentry Replay compression is off so the strict CSP does not block a blob worker, and the Sentry feedback trigger is hidden on narrow screens where it covered the hero actions. Header rows wrap up to 900px.