Buy Decentraland Names with Credits on iOS

## Summary
Community feedback (Discord, reported by cryptogreen): users want to buy Decentraland Names using Marketplace Credits inside the iOS app, similar to how Credits can already be used to buy Names on the web/desktop marketplace.

## Context
- The iOS IAP epic (#2089) and its sub-tasks (#2117, etc.) are wiring up Credits purchases for Marketplace items (wearables), but Name purchases via Credits are not currently in scope.
- User's stated motivation: they hold MANA on a BASE wallet and MANA on their Decentraland account, but can't mint a Name without first bridging/acquiring ETH for gas. Credits offer a simpler, gas-free purchase path even though they cost a premium over raw MANA price.

## Request
Extend the Credits purchase flow (once live on iOS) to also support buying Names, not just Marketplace items/wearables.

## Notes
- No existing issue found covering Names purchases via Credits on mobile.
- Related: #2089 (iOS IAP epic), #2117 (wiring iOS credits purchase to Sandbox backend)

Requested by ToxicWaifu via Slack