perf: update the logic to purchase credits (#12998)

## Description

- Replaces Stripe Checkout session flow with direct card charging for AI
credit top-ups
- Adds a two-step confirmation modal (select package → confirm purchase)
for better UX
- Creates Stripe invoice directly and charges the customer's default
payment method immediately

## Type of change

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

## How Has This Been Tested?

- Using the specs
- UI manual test cases

<img width="945" height="580" alt="image"
src="https://github.com/user-attachments/assets/52bdad46-cd0e-4927-b13f-54c6b6353bcc"
/>

<img width="945" height="580" alt="image"
src="https://github.com/user-attachments/assets/231bc7e9-41ac-440d-a93d-cba45a4d3e3e"
/>


## 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

---------

Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

app/javascript/dashboard/i18n/locale/en/settings.json

@@ -422,7 +422,15 @@
       "PURCHASE": "Purchase Credits",
       "LOADING": "Loading options...",
       "FETCH_ERROR": "Failed to load credit options. Please try again.",
-      "PURCHASE_ERROR": "Failed to process purchase. Please try again."
+      "PURCHASE_ERROR": "Failed to process purchase. Please try again.",
+      "PURCHASE_SUCCESS": "Successfully added {credits} credits to your account",
+      "CONFIRM": {
+        "TITLE": "Confirm Purchase",
+        "DESCRIPTION": "You are about to purchase {credits} credits for {amount}.",
+        "INSTANT_DEDUCTION_NOTE": "Your saved card will be charged immediately upon confirmation.",
+        "GO_BACK": "Go Back",
+        "CONFIRM_PURCHASE": "Confirm Purchase"
+      }
     }
   },
   "SECURITY_SETTINGS": {