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

assets/ts/nav.ts

@@ -36,11 +36,6 @@ const indexDispNums = Array.from(
  */
 
 export function initNav(): void {
-  const s = state.get()
-  // init threshold text
-  updateThresholdText(expand(s.threshold))
-  // init index text
-  updateIndexText(expand(s.index + 1), expand(s.length))
   // add watcher for updating nav text
   state.addWatcher((o) => {
     updateIndexText(expand(o.index + 1), expand(o.length))