add canonical link tags for all pages

Add canonical link tags in the base template.

Use .Permalink as the source and strip a trailing .html suffix so
canonical URLs are extensionless (e.g. /architecture).

Prefer extensionless canonical URLs because they are shorter and cleaner,
while the .html variants remain valid and accessible on GitHub Pages.

Canonical tags tell search engines which URL is authoritative, reducing
duplicate-URL ambiguity for indexing and ranking.

Author: ritorhymes

layouts/_default/baseof.html

@@ -4,6 +4,8 @@
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <title>{{ .Title }}</title>
+    {{- $canonical := .Permalink | replaceRE "\\.html$" "" -}}
+    <link rel="canonical" href="{{ $canonical }}">
     <link rel="icon" href="{{ relURL "favicon.ico" }}">
     {{- $style := resources.Get "sass/main.scss" | resources.ExecuteAsTemplate "main.scss" . | css.Sass }}
     <link rel="stylesheet" href="{{ $style.RelPermalink }}">