♻️ refactor(auth): inline RegisterSchema in register route

- remove external import of RegisterSchema and define it inline in the route file
- maintain same validation rules while improving code locality for the registration route

packages/auth-module/src/routes/register.route.ts

@@ -7,7 +7,7 @@ import { ErrorSchema } from '@d8d/shared-utils';
 import { AuthContext } from '@d8d/shared-types';
 import { UserSchema } from '@d8d/user-module';
 import { parseWithAwait } from '@d8d/shared-utils';
-import { RegisterSchema, TokenResponseSchema } from '../schemas';
+import { TokenResponseSchema } from '../schemas';
 
 const RegisterSchema = z.object({
   username: z.string().min(3).openapi({