fix: Create proper XML sitemap template

- Added correctly formatted sitemap.xml template in layouts/
- Includes proper XML declaration and urlset tags
- Excludes taxonomy pages that were causing issues
- Should generate valid XML instead of malformed content

Author: Debdyut

portfolio/layouts/sitemap.xml

@@ -0,0 +1,19 @@
+{{ printf "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>" | safeHTML }}
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+{{- range .Data.Pages }}
+{{- if ne .Kind "taxonomy" }}
+  <url>
+    <loc>{{ .Permalink }}</loc>
+    {{- if not .Lastmod.IsZero }}
+    <lastmod>{{ .Lastmod.Format "2006-01-02T15:04:05-07:00" }}</lastmod>
+    {{- end }}
+    {{- with .Sitemap.ChangeFreq }}
+    <changefreq>{{ . }}</changefreq>
+    {{- end }}
+    {{- if ge .Sitemap.Priority 0.0 }}
+    <priority>{{ .Sitemap.Priority }}</priority>
+    {{- end }}
+  </url>
+{{- end }}
+{{- end }}
+</urlset>