feat: BTCPay Server payment integration via pow.dgray.io proxy

AGENTS.md

@@ -61,7 +61,8 @@ js/
 │   ├── conversations.js # Zero-Knowledge Chat (E2E verschlüsselt)
 │   ├── crypto.js       # NaCl Encryption
 │   ├── currency.js     # XMR/Fiat Umrechnung
-│   └── pow-captcha.js  # Proof-of-Work Captcha (Challenge/Verify)
+│   ├── pow-captcha.js  # Proof-of-Work Captcha (Challenge/Verify)
+│   └── btcpay.js       # BTCPay Server Integration (Invoice, Checkout, Polling)
 └── components/
     ├── app-shell.js    # Layout, registriert Routes
     ├── app-header.js   # Header (Theme-Toggle, Lang-Dropdown, Profil-Dropdown)
@@ -140,7 +141,7 @@ locales/
 4. ~~PoW-Captcha server-seitig~~ ✅ PHP-Server auf `pow.dgray.io`
 5. ~~TweetNaCl self-hosted~~ ✅ In `js/vendor/`
 6. ~~Chat-Crypto fix~~ ✅ `box.before` + `secretbox`
-7. Payment-Integration mit BTCpay Server (https://pay.xmr.rocks/)
+7. ~~Payment-Integration mit BTCpay Server~~ ✅ Proxy auf `pow.dgray.io`, Frontend-Service `btcpay.js`
 8. Reputation-System (5/15/50 Deals Stufen)
 9. Push-Benachrichtigungen für neue Nachrichten