feat(billing) - facilitate top up in ai chat (#21645)

Today, when a trialing user hits their AI usage cap inside the Ask AI
chat, ending the trial bounces them to the Stripe billing portal (and,
for card-less users, loses their place in the conversation). This PR
makes activating a paid plan / topping up credits feel seamless from
within the chat:

Trial users with a card on file activate their subscription in place,
without leaving the app.
Trial users without a card are sent to the Stripe payment-method portal
and, on return, the trial is ended automatically and they're dropped
back into the exact Ask AI thread they came from.
Credit-exhaustion and trial banners now reflect whether a payment method
exists (Add Credit Card vs Subscribe Now / End Trial Period) and upgrade
inline via a confirmation modal instead of redirecting to Settings.


Uploading Screen Recording 2026-06-16 at 07.51.12.mov…


https://github.com/user-attachments/assets/4ea77273-da63-4b32-b6f1-5ac9e9560651



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packages/twenty-server/src/engine/metadata-modules/ai/utils/ai-graphql-api-exception-handler.util.ts

@@ -1,5 +1,7 @@
 import { assertUnreachable } from 'twenty-shared/utils';
 
+import { BillingException } from 'src/engine/core-modules/billing/billing.exception';
+import { billingGraphqlApiExceptionHandler } from 'src/engine/core-modules/billing/utils/billing-graphql-api-exception-handler.util';
 import {
   ConflictError,
   ForbiddenError,
@@ -13,6 +15,10 @@ import {
 } from 'src/engine/metadata-modules/ai/ai.exception';
 
 export const aiGraphqlApiExceptionHandler = (error: Error) => {
+  if (error instanceof BillingException) {
+    return billingGraphqlApiExceptionHandler(error);
+  }
+
   if (error instanceof AiException) {
     switch (error.code) {
       case AiExceptionCode.AGENT_NOT_FOUND: