fix(theme): pass TrimPrefix arguments in prefix-then-string order

strings.TrimPrefix takes the prefix first. With the arguments swapped,
resources.Get received "/" and returned the root directory, so any local
params.avatar failed the build with "only available for image resources".

themes/bonsai/layouts/partials/avatar.html

@@ -12,7 +12,7 @@
   {{- $local := false -}}
   {{- $res := "" -}}
   {{- if not $isHTTP -}}
-    {{- $clean := strings.TrimPrefix $avatar "/" -}}
+    {{- $clean := strings.TrimPrefix "/" $avatar -}}
     {{- with resources.Get $clean -}}
       {{- $res = . -}}
       {{- $local = true -}}

themes/bonsai/layouts/partials/head.html

@@ -86,7 +86,7 @@
 {{- /* Avatar preload: only for `static/`-served paths. When avatar resolves as an
        `assets/` resource the <picture> pipeline emits its own srcset/fetchpriority
        and a fixed-path preload would be wasted (different filename + format). */ -}}
-{{- if and site.Params.avatar (ne (site.Params.preloadAvatar | default true) false) (not (strings.HasPrefix site.Params.avatar "http")) (not (resources.Get (strings.TrimPrefix site.Params.avatar "/"))) }}
+{{- if and site.Params.avatar (ne (site.Params.preloadAvatar | default true) false) (not (strings.HasPrefix site.Params.avatar "http")) (not (resources.Get (strings.TrimPrefix "/" site.Params.avatar))) }}
 <link rel="preload" as="image" href="{{ site.Params.avatar | strings.TrimPrefix "/" | relURL }}" fetchpriority="high" />
 {{- end }}
 {{- /* Fingerprinted + minified CSS via Hugo's resource pipeline.