feat(web,a11y): slider accessibility improvements (#8479)

* feat(web,a11y): slider accessibility improvements

* add perceivable focus outline
* label all sliders for screen readers

* chore: add IDs to all settings sliders

* chore: add comment to id prop

* fix: switch to using CSS to add outlines

* fix: reactive sliderId

* fix: bring back the slot

* fix: add aria-describedby for the subtitle

* fix: cleanup css because disabled slider cannot be focused

* fix: add border to the slider when focus is visible

---------

Co-authored-by: Alex Tran <alex.tran1502@gmail.com>

web/src/lib/components/admin-page/settings/library-settings/library-settings.svelte

@@ -37,6 +37,7 @@
       <form autocomplete="off" on:submit|preventDefault>
         <div class="ml-4 mt-4 flex flex-col gap-4">
           <SettingSwitch
+            id="watch-filesystem"
             title="Watch filesystem"
             {disabled}
             subtitle="Watch external libraries for file changes"
@@ -64,6 +65,7 @@
       <form autocomplete="off" on:submit|preventDefault>
         <div class="ml-4 mt-4 flex flex-col gap-4">
           <SettingSwitch
+            id="periodic-library-scan"
             title="ENABLED"
             {disabled}
             subtitle="Enable periodic library scanning"