Add comprehensive unit test coverage for controllers, models, and services

- Translate French comments to English in controllers and tests
- Fix test failures: route helpers, validations, MySQL transaction issues
- Add Timecop for time-dependent tests and update database config for isolation

Gemfile.lock

@@ -381,6 +381,7 @@ GEM
     thruster (0.1.15-aarch64-linux)
     thruster (0.1.15-x86_64-darwin)
     thruster (0.1.15-x86_64-linux)
+    timecop (0.9.10)
     timeout (0.4.3)
     ttfunk (1.8.0)
       bigdecimal (~> 3.1)
@@ -452,6 +453,7 @@ DEPENDENCIES
   stimulus-rails
   stripe (~> 15.5)
   thruster
+  timecop
   turbo-rails
   tzinfo-data
   web-console