test: add tests for join mail confirmation

docs/page-permission-route-coverage.md

@@ -38,6 +38,8 @@ This document lists all protected routes, which permission set may access them,
 
 - `/auth*`, `/register`, `/reset`, `/sign-in`, `/sign-out`, `/confirm*`, `/password-reset*`, `/set_locale`
 
+The join confirmation route `GET /confirm_join/:token` is public (matched by `/confirm*`). Unit tests: `test/mv_web/controllers/join_confirm_controller_test.exs` (stubbed callback, no integration).
+
 ## Test Coverage
 
 **File:** `test/mv_web/plugs/check_page_permission_test.exs`