Fork xmrcheckout for Wownero (WOW)

Minimal changes from upstream xmrcheckout to support Wownero:
- Rate provider: Nonlogs WOW-BTC via Kraken BTC/USD
- Subaddress derivation: Wownero network byte overrides (53/63/54)
- Payment URI scheme: wownero:
- Dockerfile: Wownero binaries from Codeberg
- Display text: Monero→Wownero, XMR→WOW throughout UI
- Default daemon: 192.168.88.235:34568
- Added wownero-logo.svg

File and folder structure kept identical to upstream for easy sync.

ui/components/btcpay-modal-close-button.tsx

@@ -0,0 +1,20 @@
+"use client";
+
+export default function BtcpayModalCloseButton() {
+  const handleClick = () => {
+    if (typeof window === "undefined" || !window.parent) {
+      return;
+    }
+    window.parent.postMessage("close", "*");
+  };
+
+  return (
+    <button
+      className="rounded-full border border-stroke bg-white/80 px-3 py-1 text-[0.65rem] font-semibold uppercase tracking-[0.12em] text-ink-soft transition hover:bg-white"
+      type="button"
+      onClick={handleClick}
+    >
+      Close
+    </button>
+  );
+}