shared FlapiApiClient.testEndpoint() targets non-existent route

[jrosskopf]

Summary

FlapiApiClient.testEndpoint() (cli/shared/src/apiClient.ts:262) POSTs to /api/v1/_config/endpoints/{slug}/test. That route does not exist on the server — only /api/v1/_config/endpoints/{slug}/template/test does (src/config_service.cpp:393). Any caller would receive a 404.

The method is currently unused (the CLI's templates test correctly targets template/test via buildEndpointUrl(path, 'template/test')), but it is a latent landmine for future callers.

Fix

Point testEndpoint() at .../template/test to match the server.

Verify

A call to testEndpoint() against a live server returns 200 (not 404).

Found by docs/CLIENT_PARITY_AUDIT.md (P1).