Add OG image card and fix share receipt URL

Add 1200x630 Open Graph card with visualizer bars and feature
price tags. Use summary_large_image for Twitter. Share receipt
now uses window.location.href instead of hardcoded URL.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/app.js

@@ -403,7 +403,7 @@ function PayPlay() {
       `Actions: ${acts} (${acts > 0 ? `$${(spent/acts).toFixed(2)}/action` : "free"})`,
       `Subscriptions: ${Object.keys(subs).length}`,
       Object.keys(subs).length > 0 ? Object.keys(subs).map(k => SUBS[k].name).join(", ") : "None (cheapskate)",
-      "", "Try it: donothireus.com/payplay"
+      "", `Try it: ${window.location.href}`
     ];
     if (navigator.clipboard) {
       navigator.clipboard.writeText(lines.join("\n")).then(() => flash("Receipt copied! Share your shame.", accent));