fix(layouts): strip leading slash before relURL so subpath is honored

Hugo's relURL/absURL on a leading-slash path treats it as root-absolute
and skips the baseURL subpath. Strip the prefix first so user-supplied
paths like '/images/avatar.svg' resolve correctly under
https://*.github.io/<repo>/.

themes/bonsai/layouts/partials/bio-card.html

@@ -6,7 +6,7 @@
 
 <article class="bio">
   {{- if $avatar }}
-  <img class="bio__avatar" src="{{ $avatar | absURL }}" alt="{{ $name }}" loading="eager" />
+  <img class="bio__avatar" src="{{ $avatar | strings.TrimPrefix "/" | relURL }}" alt="{{ $name }}" loading="eager" />
   {{- end }}
 
   <h1 class="bio__name">{{ $name }}</h1>

themes/bonsai/layouts/partials/head.html

@@ -20,8 +20,8 @@
 {{- end }}
 <meta name="twitter:card" content="summary" />
 
-<link rel="icon" href="{{ (site.Params.favicon | default `/favicon.ico`) | absURL }}" />
-<link rel="stylesheet" href="{{ `css/bonsai.css` | absURL }}" />
+<link rel="icon" href="{{ (site.Params.favicon | default `favicon.ico`) | strings.TrimPrefix "/" | relURL }}" />
+<link rel="stylesheet" href="{{ `css/bonsai.css` | relURL }}" />
 {{- if site.Params.themeToggle }}
-<script defer src="{{ `js/theme-toggle.js` | absURL }}"></script>
+<script defer src="{{ `js/theme-toggle.js` | relURL }}"></script>
 {{- end }}