feat: complete v1 — QR invoice generator with i18n, short URLs, offline support

- XMR address validation (standard, subaddress, integrated)
- Amount in XMR/EUR/USD/CHF with CoinGecko conversion
- QR code generation with monero: URI
- Shareable short URLs (/s/abc123) via self-hosted PHP backend
- i18n (DE/EN) with browser language detection
- Service worker for offline capability
- Dark mode, responsive design

s.php

@@ -0,0 +1,28 @@
+<?php
+$code = trim($_SERVER['PATH_INFO'] ?? $_GET['c'] ?? '', '/');
+
+if (empty($code) || !preg_match('/^[a-z0-9]{4,10}$/', $code)) {
+    http_response_code(404);
+    echo 'Not found';
+    exit;
+}
+
+$dbFile = __DIR__ . '/data/urls.json';
+if (!file_exists($dbFile)) {
+    http_response_code(404);
+    echo 'Not found';
+    exit;
+}
+
+$urls = json_decode(file_get_contents($dbFile), true) ?: [];
+
+if (!isset($urls[$code])) {
+    http_response_code(404);
+    echo 'Not found';
+    exit;
+}
+
+$hash = $urls[$code];
+$base = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] === 'on' ? 'https' : 'http') . '://' . $_SERVER['HTTP_HOST'];
+header('Location: ' . $base . '/#' . $hash, true, 302);
+exit;