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/dashboard/i18n/locale/en/signup.json

@@ -45,6 +45,13 @@
       "ERROR_MESSAGE": "Could not connect to Woot server. Please try again."
     },
     "SUBMIT": "Create account",
-    "HAVE_AN_ACCOUNT": "Already have an account?"
+    "HAVE_AN_ACCOUNT": "Already have an account?",
+    "VERIFY_EMAIL": {
+      "TITLE": "Check your inbox",
+      "DESCRIPTION": "We sent a verification link to {email}. Click the link to verify your email and get started.",
+      "RESEND": "Resend verification email",
+      "RESEND_SUCCESS": "Verification email sent. Please check your inbox.",
+      "RESEND_ERROR": "Could not send verification email. Please try again."
+    }
   }
 }