[codex] restrict source additions to default project

[thepluck]

Summary

• add a Default project selector that switches the form back to the default project flow without creating a project
• disable source file inputs and Add Source while a custom project is selected
• add browser coverage for custom-project source controls being disabled

Tests

• yarn build
• yarn lint
• yarn test:browser
• git diff --check

[Copilot]

Pull request overview

This PR tightens the simulation request UI so that source file additions are only possible when the “default project” flow is selected, adding an explicit “Default” selector to return from a custom project back to the default flow.

Changes:

• Add a “Default” project selector and track the active default-project path to support switching back without creating a new project.
• Disable Source File / Source inputs and the “Add Source” action while a custom project is selected.
• Add Playwright browser coverage to verify source controls are disabled for custom projects and re-enabled when switching back to default.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
frontend/tests/simulation-ui.spec.ts	Updates existing UI expectation for the new “Default” button and adds a new browser test ensuring source controls are disabled for custom projects.
frontend/src/styles/request.css	Expands the project browse field grid layout to accommodate the new “Default” button.
frontend/src/features/request/RequestForm.tsx	Implements default-project selection logic, disables source controls for custom projects, and wires up the new “Default” selector.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.