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/i18n/locale/en/settings.json

@@ -467,7 +467,18 @@
       "TITLE": "Current Plan",
       "PLAN_NOTE": "You are currently subscribed to the **{plan}** plan with **{quantity}** licenses",
       "SEAT_COUNT": "Number of seats",
-      "RENEWS_ON": "Renews on"
+      "RENEWS_ON": "Renews on",
+      "CURRENCY": "Currency"
+    },
+    "CURRENCY": {
+      "SELECT": {
+        "TITLE": "Choose your billing currency",
+        "DESCRIPTION": "Select the currency you'd like to be billed in. This can't be changed once your subscription is created."
+      },
+      "OPTIONS": {
+        "USD": "US Dollar (USD)",
+        "BRL": "Brazilian Real (BRL)"
+      }
     },
     "VIEW_PRICING": "View Pricing",
     "MANAGE_SUBSCRIPTION": {
@@ -503,6 +514,7 @@
       "PURCHASE": "Purchase Credits",
       "LOADING": "Loading options...",
       "FETCH_ERROR": "Failed to load credit options. Please try again.",
+      "RETRY": "Retry",
       "PURCHASE_ERROR": "Failed to process purchase. Please try again.",
       "PURCHASE_SUCCESS": "Successfully added {credits} credits to your account",
       "CONFIRM": {