feat(checkout): FUNDEDBIT 2-step checkout redesign — dynamic, native payment, add-on only

[kautzargypf]

Summary

Rebuilds the checkout into the FUNDEDBIT 2-step design (Challenge → Information),
delivered entirely as the yourpropfirm-ui-addon override layer. Runs against the
stock main plugin 1.15 + this add-on — zero main-plugin changes. Everything in
Step 1 and the order summary is driven by the merchant's WooCommerce categories,
products and gateways — nothing hardcoded.

Reported bugs fixed

Bug (from staging)	Fix
Continue button can't be selected	Plugin 1.15 removed checkout-multistep.js; the add-on now owns the 2-step engine (6930949)
Product Category & Account empty in order summary	Derive from real store data + leaf category (eb9b2ab)
Currency not following WooCommerce	Use get_woocommerce_currency() + store currency format (eb9b2ab)

What's included

• Step 1 (Challenge): category-driven, design-matched — eval-type cards (name +
  description + badge + radio dot), account-balance pills, trading platform. All read live
  from categories/products (3841096).
• Drill-down render fix: the category/product picker no longer collapses to a blank
  column (5b11570).
• Step 2 (Information): email sub-step → billing → native WooCommerce payment using
  the merchant's own enabled gateways (dynamic #payment_method_select); each gateway
  renders its own fields (e.g. Stripe card form); "Proceed to Payment" places the order via
  native WC. Terms handled via consent text (hidden accepted terms field) — no
  checkbox (948e4a1).
• Currency model: account balance follows the product's Account Currency; prices
  follow the store currency (b9bf550).
• Order-summary nav: removed the redundant Back button to match the design (eb1e795).
• Admin "Checkout Badge" field on Product Categories so "Best Value"/"Most Popular" are
  editable in admin, not just code (00fc094).
• setup_guide.md — production configuration reference.

Testing

• End-to-end verified locally on plugin 1.15: Stripe test card → order placed →
  order-received page; all order details dynamic from the WC order.
• Verified with EUR store currency + USD account currency (account shows $, prices €).

Notes for deployment

• See setup_guide.md for product/category structure, checkout settings, gateways,
  terms, and the currency model.
• Compiled dist/css/checkout.css is committed — no Node build needed in production.
• The main plugin caches checkout data ~5 min; product/category edits may take a refresh to
  appear.

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