[mod] client/simple: client plugins (#5406)

* [mod] client/simple: client plugins

Defines a new interface for client side *"plugins"* that coexist with server
side plugin system. Each plugin (e.g., `InfiniteScroll`) extends the base
`ts Plugin`. Client side plugins are independent and lazy‑loaded via `router.ts`
when their `load()` conditions are met. On each navigation request, all
applicable plugins are instanced.

Since these are client side plugins, we can only invoke them once DOM is fully
loaded. E.g. `Calculator` will not render a new `answer` block until fully
loaded and executed.

For some plugins, we might want to handle its availability in `settings.yml`
and toggle in UI, like we do for server side plugins. In that case, we extend
`py Plugin` instancing only the information and then checking client side if
[`settings.plugins`](https://github.com/inetol/searxng/blob/1ad832b1dc33f3f388da361ff2459b05dc86a164/client/simple/src/js/toolkit.ts#L134)
array has the plugin id.

* [mod] client/simple: rebuild static

searx/settings.yml

@@ -124,8 +124,6 @@ ui:
   # query_in_title: When true, the result page's titles contains the query
   # it decreases the privacy, since the browser can records the page titles.
   query_in_title: false
-  # infinite_scroll: When true, automatically loads the next page when scrolling to bottom of the current page.
-  infinite_scroll: false
   # ui theme
   default_theme: simple
   # center the results ?
@@ -162,7 +160,6 @@ ui:
 #     - locale
 #     - theme
 #     - results_on_new_tab
-#     - infinite_scroll
 #     - search_on_category_select
 #     - method
 #     - image_proxy
@@ -214,6 +211,7 @@ outgoing:
   #    - 1.1.1.2
   #    - fe80::/126
 
+
 # Plugin configuration, for more details see
 #   https://docs.searxng.org/admin/settings/settings_plugins.html
 #
@@ -222,6 +220,9 @@ plugins:
   searx.plugins.calculator.SXNGPlugin:
     active: true
 
+  searx.plugins.infinite_scroll.SXNGPlugin:
+    active: false
+
   searx.plugins.hash_plugin.SXNGPlugin:
     active: true