refactor: remove username from User model, login by email only

tests/unit/app/users/user-form-pages.test.ts

@@ -74,7 +74,6 @@ describe("new user form localization", () => {
 
     // Form labels from dictionary
     expect(html).toContain("Nombre")
-    expect(html).toContain("Usuario")
     expect(html).toContain("Correo electrónico")
     expect(html).toContain("Contraseña")
     expect(html).toContain("Rol")
@@ -104,7 +103,6 @@ describe("new user form localization", () => {
 
     expect(html).toContain("New User")
     expect(html).toContain("Full name")
-    expect(html).toContain("Username")
     expect(html).toContain("Password")
     expect(html).toContain("Minimum 8 characters")
     expect(html).toContain("Create User")
@@ -136,7 +134,6 @@ describe("edit user form localization", () => {
     mocks.getUserProfileById.mockResolvedValue({
       id: "user-1",
       name: "Ada Lovelace",
-      username: "ada",
       email: "ada@example.test",
       role: "ADMIN",
       isActive: true,