docs: add SEO improvements — robots.txt, sitemap.xml, canonical URL, structured data

docs/index.html

@@ -13,7 +13,23 @@
   <meta name="twitter:description" content="A sleek, dark-themed webchat UI for OpenClaw. Monitor sessions, stream responses, and inspect tool calls in real-time." />
   <meta name="twitter:image" content="https://raw.githubusercontent.com/MarlBurroW/pinchchat/main/public/og-card.png" />
   <meta property="og:url" content="https://marlburrow.github.io/pinchchat/" />
+  <link rel="canonical" href="https://marlburrow.github.io/pinchchat/" />
+  <meta name="robots" content="index, follow" />
   <link rel="icon" type="image/png" href="https://raw.githubusercontent.com/MarlBurroW/pinchchat/main/public/logo.png" />
+  <script type="application/ld+json">
+  {
+    "@context": "https://schema.org",
+    "@type": "SoftwareApplication",
+    "name": "PinchChat",
+    "description": "A sleek, dark-themed webchat UI for OpenClaw. Monitor sessions, stream responses, and inspect tool calls in real-time.",
+    "url": "https://marlburrow.github.io/pinchchat/",
+    "applicationCategory": "DeveloperApplication",
+    "operatingSystem": "Web",
+    "license": "https://opensource.org/licenses/MIT",
+    "codeRepository": "https://github.com/MarlBurroW/pinchchat",
+    "offers": { "@type": "Offer", "price": "0", "priceCurrency": "USD" }
+  }
+  </script>
   <style>
     @import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&display=swap');