[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

docs/admin/settings/settings_plugins.rst

@@ -69,6 +69,9 @@ The built-in plugins are all located in the namespace `searx.plugins`.
       searx.plugins.calculator.SXNGPlugin:
         active: true
 
+      searx.plugins.infinite_scroll.SXNGPlugin:
+        active: false
+
       searx.plugins.hash_plugin.SXNGPlugin:
         active: true
 

docs/admin/settings/settings_ui.rst

@@ -12,7 +12,6 @@
    ui:
      default_locale: ""
      query_in_title: false
-     infinite_scroll: false
      center_alignment: false
      cache_url: https://web.archive.org/web/
      default_theme: simple
@@ -32,9 +31,6 @@
   When true, the result page's titles contains the query it decreases the
   privacy, since the browser can records the page titles.
 
-``infinite_scroll``:
-  When true, automatically loads the next page when scrolling to bottom of the current page.
-
 ``center_alignment`` : default ``false``
   When enabled, the results are centered instead of being in the left (or RTL)
   side of the screen.  This setting only affects the *desktop layout*

docs/dev/plugins/builtins.rst

@@ -10,6 +10,7 @@ Built-in Plugins
    calculator
    hash_plugin
    hostnames
+   infinite_scroll
    self_info
    tor_check
    unit_converter

docs/dev/plugins/infinite_scroll.rst

@@ -0,0 +1,8 @@
+.. _plugins.infinite_scroll:
+
+===============
+Infinite scroll
+===============
+
+.. automodule:: searx.plugins.infinite_scroll
+   :members: