Build an API v2 simulation console in app v2

The original request was to migrate the legacy API v1 simulation tool from https://legacy.policyengine.org/us/developer-tools/simulations. Do not port that API v1 implementation. Build the replacement after the API v2 simulation and calculation contract is stable.

Scope

• Add a country-scoped /[countryId]/dev-tools/simulations route in the Next.js application.
• Accept and edit a typed API v2 simulation or calculation request.
• Support the authentication required by the finalized API v2 endpoint.
• Submit asynchronous work, poll its status, and display the completed response or structured error.
• Show the request and response payloads in a format suitable for API debugging.
• Add the simulation console to /[countryId]/dev-tools.
• Redirect the former /[countryId]/developer-tools/simulations path to the replacement route.
• Add tests for request validation, authentication errors, polling completion, API errors, and country-specific routing.

Timing

Defer implementation until the API v2 request, authentication, job-status, and response schemas are stable.