Add unit tests for platform web

## Summary
Add unit test coverage for the platform web service.

## Scope
- Cover web route handlers.
- Cover API client behavior with test servers/mocks.
- Cover form validation and request/response handling for admin flows.
- Ensure web handlers continue to call the API instead of querying the database directly.

## Acceptance Criteria
- Key web routes have unit tests for expected responses and redirects.
- Admin form handling has tests for valid and invalid submissions.
- API client calls are tested without depending on a live API service.
- `go test ./...` remains passing.

Start by locating the platform web route handlers, API client, and admin form handling described in the issue. Add isolated tests for route responses and redirects, valid and invalid admin submissions, and API calls using test servers or mocks; run `go test ./...` to confirm the suite passes without a live API.

Written by the indexing model from the issue text.