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

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

web/src/lib/components/user-settings-page/memories-settings.svelte

@@ -36,6 +36,7 @@
       <div class="ml-4 mt-4 flex flex-col gap-4">
         <div class="ml-4">
           <SettingSwitch
+            id="time-based-memories"
             title="Time-based memories"
             subtitle="Photos from previous years"
             bind:checked={user.memoriesEnabled}