Add SEO baseline: robots.txt, sitemap.xml, canonical, OG/Twitter tags, JSON-LD

Fixes missing crawler/social metadata so search engines and link
previews can index and render the page correctly.

index.html

@@ -14,7 +14,33 @@
       content="15+ years of CaseWare/CaseView development, client templates, and release automation."
     />
     <meta property="og:type" content="website" />
+    <meta property="og:url" content="https://caseware.levkin.ca/" />
+    <meta property="og:site_name" content="Ilia Dobkin — CaseWare Development" />
+    <meta name="twitter:card" content="summary" />
+    <meta name="twitter:title" content="Ilia Dobkin — CaseWare & CaseView Development" />
+    <meta
+      name="twitter:description"
+      content="Senior CaseWare/CaseView developer with 15+ years building audit and financial reporting solutions."
+    />
+    <link rel="canonical" href="https://caseware.levkin.ca/" />
     <link rel="icon" href="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 32 32'%3E%3Crect width='32' height='32' rx='6' fill='%230d2840'/%3E%3Cpath d='M9 11h14M9 16h14M9 21h9' stroke='%23c9a861' stroke-width='2.5' stroke-linecap='round'/%3E%3C/svg%3E" />
+    <script type="application/ld+json">
+      {
+        "@context": "https://schema.org",
+        "@type": "ProfessionalService",
+        "name": "Ilia Dobkin — CaseWare Development",
+        "url": "https://caseware.levkin.ca/",
+        "description": "Senior CaseWare/CaseView developer with 15+ years building audit and financial reporting solutions for CaseWare International, MNP, Jazz, and accounting firms.",
+        "email": "idobkin@gmail.com",
+        "areaServed": "North America",
+        "sameAs": [
+          "https://levkin.ca/",
+          "https://auto.levkin.ca/",
+          "https://iliadobkin.com/",
+          "https://www.linkedin.com/in/ilia-dobkin-8263343/"
+        ]
+      }
+    </script>
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <link