feat: add canonical tag

- https://developer.mozilla.org/en-US/docs/Web/HTML/Link_types

themes/chameleon/layout/_partial/head.ejs

@@ -22,6 +22,7 @@
   %>
   <title><% if (title) { %><%= title %> | <% } %><%= config.title %></title>
   <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
+  <link rel="canonical" href="<%- full_url_for(path) %>">
   <%/* Add Open Graph meta tags for easier sharing on social networking sites */%>
   <%/* Modified from original source for compatibility with my blog */%>
   <%- openGraph() %>