refactor(api): refactor API module with route definitions and response utilities

Restructure the core API module to improve clarity, consistency, and
maintainability:

- Introduce `defineApiRoutes()` helper for declarative route definitions
  with built-in config validation at startup
- Add `apiSuccess()` / `apiError()` response utilities; enforce their
  use across all handlers (core and modules)
- Move auth enforcement to route definitions (`auth: 'public' | 'user' |
  'admin'`), removing manual auth checks from handlers
- Extract core routes into `core-routes.js`; router now has no knowledge
  of specific features
- Rename `nx-route.js` to `route-handler.js` and update package.json
  export accordingly
- Update ARCHITECTURE.md to reflect new API conventions and point to
  `src/core/api/README.md` for details

docs/dev/LANGUE.md

@@ -16,22 +16,6 @@ Tout ce qui est **visible par l'utilisateur** est en **français** :
 - Slugs et noms de dossiers qui correspondent à des routes URL
 - Documentations, README.md
 
-## Messages de commit Git
-
-Tous les messages de commit doivent être rédigés en **anglais**, en suivant le format conventional commits :
-
-```
-<type>(<scope>): <description courte>
-```
-
-Types courants : `feat`, `fix`, `refactor`, `style`, `docs`, `test`, `chore`
-
-Exemples :
-- `feat(auth): add OAuth2 login support`
-- `fix(api): handle null response from payment gateway`
-- `docs(guide): add git commit message conventions`
-- `chore(deps): update dependencies`
-
 ## Guide de rédaction
 
 Se référer à `REDACTION.md` avant de rédiger tout contenu textuel.