feat: embed threshold and index val of navbar into html/inline js (#241)

* feat: refactor image retrieval logic and improve variable initialization

- Add a new file `layouts/partials/function/getImageSlice.html`
- Initialize variables `$context`, `$Path`, and `$params`
- Set `$Path` based on the result of the `partial/function/currentMenuItem.html` partial
- Retrieve the page `$gallery` based on `$Path`
- Return all resources of type `image` from `$gallery`

* refactor: adapt getImageSlice function to `single.json`

* feat: refactor navigation UI components to use static go template

* feat: update navigation functionality and threshold rendering

layouts/_default/single.json

@@ -1,15 +1,9 @@
-{{- $Page := . -}}
-{{- $Path := "" -}}
+{{- $context := . -}}
 {{- $params := .Page.Params | merge .Site.Params.Page -}}
 
-{{- with partial "function/currentMenuItem.html" . -}}
-  {{- $Path = .Identifier -}}
-{{- end -}}
-
-{{- $gallery := site.GetPage $Path -}}
-{{- with $gallery.Resources.ByType "image" -}}
+{{- with partial "function/getImageSlice.html" .  -}}
   {{- $index := len . -}}
-  {{- $Page.Scratch.Add "img" slice -}}
+  {{- $context.Scratch.Add "img" slice -}}
   {{- range sort . "Name" "desc" -}}
     {{- $image := . -}}
     {{- $index = sub $index 1 -}}
@@ -19,7 +13,7 @@
     {{- end -}}
     {{- $lores := .Resize (site.Params.loResOpt | default "700x webp Lanczos q60") -}}
     {{- $hires := .Resize (site.Params.hiResOpt | default "2000x webp Lanczos q75") -}}
-    {{- $Page.Scratch.Add "img" (dict
+    {{- $context.Scratch.Add "img" (dict
       "index" (int $index)
       "alt" (string $alt)
       "loUrl" (string $lores.RelPermalink)
@@ -31,7 +25,7 @@
       )
     -}}
   {{- end -}}
-    {{ $Page.Scratch.Get "img" | jsonify }}
+    {{ $context.Scratch.Get "img" | jsonify }}
 {{- else -}}
 []
 {{- end -}}