fix: read the merchant name from lunar.checkout.merchant

[alecritson]

Problem

CheckoutServiceProvider merges config/checkout.php under lunar.checkout, but three places read checkout.merchant:

• the checkout header prop (CheckoutController::projectCheckout)
• the root view's tab title (app.blade.php)
• spec 0008

So CHECKOUT_MERCHANT, and a merchant set in a published config/lunar/checkout.php, were never used. The header always fell back to app.name. It only worked in Edwardes because the app sets config(['checkout.merchant' => ...]) directly. The tests set the same wrong key, so they passed anyway.

The processing page was separate: it rendered config('app.name', 'Store') and ignored the setting, so its header could show a different name from the checkout's.

Change

• One private merchant() helper on the controller: lunar.checkout.merchant, falling back to app.name. Used by both the checkout and processing pages.
• The root view's tab title reads lunar.checkout.merchant.
• The tests and spec 0008 now use the real key.

Payment methods

I also checked what happens when a store installs checkout before it registers any payment method. It already behaves well: the page renders, the payment section shows "No payment methods are available." with pay disabled, and pay returns 422. A new test covers that, since none did.

Testing

• The existing merchant tests now set lunar.checkout.merchant. On the old code, the header test fails.
• New: the processing page shows the configured merchant. It fails on the old code and passes with the fix.
• New: the checkout renders with no payment methods registered, and pay refuses with 422.
• Full suite: 268 passed, 1 skipped. pint and phpstan are clean.

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