test(bruno): update API tests to use @tests.bookhoard.internal

Update test email domain in Bruno API collection files:
- Login User.yml
- Register User.yml
- Update Profile.yml

Ensures API tests use the dedicated test domain and won't conflict
with real user data when developers run tests.

bruno/user/auth/Login User.yml

@@ -10,7 +10,7 @@ http:
     type: json
     data: |-
       {
-        "login": "testuser@example.com",
+        "login": "testuser@tests.bookhoard.internal",
         "password": "Test@Pass123!"
       }
 

bruno/user/auth/Register User.yml

@@ -11,7 +11,7 @@ http:
     data: |-
       {
         "username": "testuser",
-        "email": "testuser@example.com",
+        "email": "testuser@tests.bookhoard.internal",
         "password": "Test@Pass123!",
         "first_name": "Test",
         "last_name": "User"

bruno/user/profile/Update Profile.yml

@@ -11,7 +11,7 @@ http:
     jsonBody: |-
       {
         "username": "updateduser",
-        "email": "updated@example.com",
+        "email": "updated@tests.bookhoard.internal",
         "first_name": "Updated",
         "last_name": "User",
         "theme": "dracula"