feat: ensure signup verification [UPM-14] (#13858)

Previously, signing up gave immediate access to the app. Now,
unconfirmed users are redirected to a verification page where they can
resend the confirmation email.

- After signup, the user is routed to `/auth/verify-email` instead of
the dashboard
- After login, unconfirmed users are redirected to the verification page
- The dashboard route guard catches unconfirmed users and redirects them
- `active_for_authentication?` is removed from the sessions controller
so unconfirmed users can authenticate — the frontend gates access
instead
- If the user visits the verification page after already confirming,
they're automatically redirected to the dashboard
- No session is issued until the user is verified

<details><summary>Demo</summary>
<p>

#### Fresh Signup


https://github.com/user-attachments/assets/abb735e5-7c8e-44a2-801c-96d9e4823e51

#### Google Fresh Signup


https://github.com/user-attachments/assets/ab9e389a-a604-4a9d-b492-219e6d94ee3f


#### Create new account from Dashboard


https://github.com/user-attachments/assets/c456690d-1946-4e0b-834b-ad8efcea8369



</p>
</details>

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/javascript/v3/views/auth/signup/components/Signup/Form.vue

@@ -4,8 +4,8 @@ import { useVuelidate } from '@vuelidate/core';
 import { required, minLength, email } from '@vuelidate/validators';
 import { useStore } from 'vuex';
 import { useI18n } from 'vue-i18n';
+import { useRouter } from 'vue-router';
 import { useAlert } from 'dashboard/composables';
-import { DEFAULT_REDIRECT_URL } from 'dashboard/constants/globals';
 import VueHcaptcha from '@hcaptcha/vue3-hcaptcha';
 import FormInput from '../../../../../components/Form/Input.vue';
 import NextButton from 'dashboard/components-next/button/Button.vue';
@@ -19,6 +19,7 @@ const MIN_PASSWORD_LENGTH = 6;
 
 const store = useStore();
 const { t } = useI18n();
+const router = useRouter();
 
 const hCaptcha = ref(null);
 const isPasswordFocused = ref(false);
@@ -76,7 +77,10 @@ const performRegistration = async () => {
   isSignupInProgress.value = true;
   try {
     await register(credentials);
-    window.location = DEFAULT_REDIRECT_URL;
+    router.push({
+      name: 'auth_verify_email',
+      state: { email: credentials.email },
+    });
   } catch (error) {
     const errorMessage = error?.message || t('REGISTER.API.ERROR_MESSAGE');
     if (globalConfig.value.hCaptchaSiteKey) {