feat: PDF invoice, payment summary, UI polish

- PDF invoice generation with jsPDF (lazy-loaded, includes paid status)
- Payment summary card: amount, fiat equivalent, description prominently displayed
- URI box hidden behind collapsible "Show Monero URI" details
- Smart countdown: "29 Tage, 23 Std." instead of ticking seconds
- Dynamic page title: "0.017 XMR — Rechnung #42 | xmrpay.link"
- Result card fade-in animation
- Responsive QR code on mobile
- Rename .btn-monitor to .btn-proof
- "In Wallet öffnen" unified as <button>

i18n.js

@@ -20,14 +20,25 @@ var I18n = (function () {
       btn_generate: 'Zahlungsanforderung erstellen',
       btn_open_wallet: 'In Wallet öffnen',
       btn_copy_addr: 'Adresse kopieren',
+      btn_download_pdf: 'PDF Rechnung',
+      pdf_title: 'Zahlungsanforderung',
+      pdf_address: 'XMR-Adresse',
+      pdf_amount: 'Betrag',
+      pdf_desc: 'Beschreibung',
+      pdf_deadline: 'Zahlungsfrist',
+      pdf_deadline_days: '{d} Tage',
+      pdf_date: 'Datum',
+      pdf_scan_qr: 'QR-Code scannen zum Bezahlen',
+      pdf_footer: 'Erstellt mit xmrpay.link — Keine Registrierung, kein KYC',
       qr_hint: 'Klick auf QR zum Speichern',
       footer: 'Open Source &middot; Kein Backend &middot; Kein KYC &middot; <a href="https://gitea.schmidt.eco/schmidt1024/xmrpay.link" target="_blank">Source</a>',
+      label_uri_details: 'Monero-URI anzeigen',
       label_share_link: 'Teilbarer Link',
       btn_new_request: 'Neue Zahlungsanforderung',
       toast_copied: 'Kopiert!',
       countdown_expired: 'Zahlungsfrist abgelaufen',
-      countdown_remaining_days: 'Zahlungsfrist: {d} Tage, {h}:{m}:{s}',
-      countdown_remaining_hours: 'Zahlungsfrist: {h}:{m}:{s}',
+      countdown_remaining_days: 'Zahlungsfrist: {d} Tage, {h} Std.',
+      countdown_remaining_hours: 'Zahlungsfrist: {h}:{m} Std.',
       rates_offline: 'Kurse nicht verfügbar — nur XMR-Betrag möglich',
       btn_prove_payment: 'Zahlung nachweisen',
       label_tx_hash: 'Transaction ID (TX Hash)',
@@ -55,14 +66,25 @@ var I18n = (function () {
       btn_generate: 'Create payment request',
       btn_open_wallet: 'Open in wallet',
       btn_copy_addr: 'Copy address',
+      btn_download_pdf: 'PDF Invoice',
+      pdf_title: 'Payment Request',
+      pdf_address: 'XMR Address',
+      pdf_amount: 'Amount',
+      pdf_desc: 'Description',
+      pdf_deadline: 'Payment deadline',
+      pdf_deadline_days: '{d} days',
+      pdf_date: 'Date',
+      pdf_scan_qr: 'Scan QR code to pay',
+      pdf_footer: 'Created with xmrpay.link — No registration, no KYC',
       qr_hint: 'Click QR to save',
       footer: 'Open Source &middot; No Backend &middot; No KYC &middot; <a href="https://gitea.schmidt.eco/schmidt1024/xmrpay.link" target="_blank">Source</a>',
+      label_uri_details: 'Show Monero URI',
       label_share_link: 'Shareable link',
       btn_new_request: 'New payment request',
       toast_copied: 'Copied!',
       countdown_expired: 'Payment deadline expired',
-      countdown_remaining_days: 'Deadline: {d} days, {h}:{m}:{s}',
-      countdown_remaining_hours: 'Deadline: {h}:{m}:{s}',
+      countdown_remaining_days: 'Deadline: {d} days, {h} hrs',
+      countdown_remaining_hours: 'Deadline: {h}:{m} hrs',
       rates_offline: 'Rates unavailable — XMR amount only',
       btn_prove_payment: 'Prove payment',
       label_tx_hash: 'Transaction ID (TX Hash)',