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/controllers/api/v1/accounts_controller.rb

@@ -31,8 +31,18 @@ class Api::V1::AccountsController < Api::BaseController
       user: current_user
     ).perform
     if @user
-      send_auth_headers(@user)
-      render 'api/v1/accounts/create', format: :json, locals: { resource: @user }
+      # Authenticated users (dashboard "add account") and api_only signups
+      # need the full response with account_id. API-only deployments have no
+      # frontend to handle the email confirmation flow, so they need auth
+      # tokens to proceed.
+      # Unauthenticated web signup returns only the email — no session is
+      # created until the user confirms via the email link.
+      if current_user || api_only_signup?
+        send_auth_headers(@user)
+        render 'api/v1/accounts/create', format: :json, locals: { resource: @user }
+      else
+        render json: { email: @user.email }
+      end
     else
       render_error_response(CustomExceptions::Account::SignupFailed.new({}))
     end
@@ -103,6 +113,15 @@ class Api::V1::AccountsController < Api::BaseController
     raise ActionController::RoutingError, 'Not Found' unless GlobalConfigService.account_signup_enabled?
   end
 
+  def api_only_signup?
+    # CW_API_ONLY_SERVER is the canonical flag for API-only deployments.
+    # ENABLE_ACCOUNT_SIGNUP='api_only' is a legacy sentinel for the same purpose.
+    # Read ENABLE_ACCOUNT_SIGNUP raw from InstallationConfig because GlobalConfig.get
+    # typecasts it to boolean, coercing 'api_only' to true.
+    ActiveModel::Type::Boolean.new.cast(ENV.fetch('CW_API_ONLY_SERVER', false)) ||
+      InstallationConfig.find_by(name: 'ENABLE_ACCOUNT_SIGNUP')&.value.to_s == 'api_only'
+  end
+
   def validate_captcha
     raise ActionController::InvalidAuthenticityToken, 'Invalid Captcha' unless ChatwootCaptcha.new(params[:h_captcha_client_response]).valid?
   end