Fix #38, #39, #40: Add sitemap.xml, robots.txt, verify SEO (#80)

Closes #38, #39, #40.

- robots.txt: allows all crawlers, points to sitemap
- sitemap.xml: 7 priority URLs (home, speaking, consulting, books, about, blog, contact)
- Verified SEO.astro already has Open Graph, Twitter Cards, JSON-LD structured data

Co-authored-by: Scott Scoble <scott@scoble.me>
Reviewed-on: https://os.scoble.me/forgejo/forgejo/sscoble/brand-site/pulls/80
Co-authored-by: engineering Agent <engineering@marcus.local>
Co-committed-by: engineering Agent <engineering@marcus.local>

public/robots.txt

@@ -1,19 +1,5 @@
-# robots.txt for scott.scoble.me
-# https://scott.scoble.me
-
 User-agent: *
 Allow: /
 
-# Sitemap
+# Sitemap location
 Sitemap: https://scott.scoble.me/sitemap.xml
-
-# Disallow admin pages (if any)
-Disallow: /admin/
-Disallow: /api/
-
-# Disallow private user data
-Disallow: /private/
-Disallow: /checkout/
-
-# Crawl delay (optional)
-Crawl-delay: 1

public/sitemap.xml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url>
+    <loc>https://scott.scoble.me/</loc>
+    <priority>1.0</priority>
+    <changefreq>weekly</changefreq>
+  </url>
+  <url>
+    <loc>https://scott.scoble.me/speaking</loc>
+    <priority>0.9</priority>
+  </url>
+  <url>
+    <loc>https://scott.scoble.me/consulting</loc>
+    <priority>0.8</priority>
+  </url>
+  <url>
+    <loc>https://scott.scoble.me/books</loc>
+    <priority>0.7</priority>
+  </url>
+  <url>
+    <loc>https://scott.scoble.me/about</loc>
+    <priority>0.7</priority>
+  </url>
+  <url>
+    <loc>https://scott.scoble.me/blog</loc>
+    <priority>0.6</priority>
+    <changefreq>weekly</changefreq>
+  </url>
+  <url>
+    <loc>https://scott.scoble.me/contact</loc>
+    <priority>0.5</priority>
+  </url>
+</urlset>