feat: billing brl pix new users (#14617)

## Linear ticket
- https://linear.app/chatwoot/issue/CW-7253/billing-brl-pix-new-users

## Description

New accounts that sign up in Brazilian Portuguese are now billed in BRL
instead of USD. Their Stripe customer is created with a Brazil address
and Portuguese locale (so the Stripe portal offers Real prices and PIX),
and the AI credit top-up flow shows packages priced in the account's
billing currency. Currency support is config-driven, so adding another
currency later is a configuration change rather than a code change.


## Type of change

- [ ] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

- https://www.loom.com/share/c8d3d08c1b844ed6b820438d4209491a

## Screenshot
<img width="904" height="440" alt="image"
src="https://github.com/user-attachments/assets/6f19fad8-e6af-46ea-b99f-b0265bb9eeec"
/>


## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/api/enterprise/account.js

@@ -14,6 +14,10 @@ class EnterpriseAccountAPI extends ApiClient {
     return axios.post(`${this.url}subscription`);
   }
 
+  selectBillingCurrency(currency) {
+    return axios.post(`${this.url}select_billing_currency`, { currency });
+  }
+
   getLimits() {
     return axios.get(`${this.url}limits`);
   }
@@ -27,6 +31,11 @@ class EnterpriseAccountAPI extends ApiClient {
   createTopupCheckout(credits) {
     return axios.post(`${this.url}topup_checkout`, { credits });
   }
+
+  // Topup packages for the account's billing currency.
+  getTopupOptions() {
+    return axios.get(`${this.url}topup_options`);
+  }
 }
 
 export default new EnterpriseAccountAPI();