feat(web,a11y): standardize the FullScreenModal UI (#8566)

* feat(web,a11y): standardize the FullScreenModal look

* consistent header, padding, close button, and radius as BaseModal
* vertically stacking ConfirmDialogue CTA buttons in narrow screens
* adding aria-modal tags for screen reader
* add viewport-specific height limits on modals, to enable scrolling
* prevent focus from being hidden under sticky content in modals
* standardize FullScreenModal widths using a Prop

* wip: consistent padding with header

* fix: alignment on "create user" and "edit user" modals

* fix: horizontal modal content alignment

* fix: create user CTA buttons

* chore: remove unnecessary warning

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Co-authored-by: Jason Rasmussen <jrasm91@gmail.com>

web/src/routes/admin/library-management/+page.svelte

@@ -302,6 +302,7 @@
 
 {#if confirmDeleteLibrary}
   <ConfirmDialogue
+    id="warning-modal"
     title="Warning!"
     prompt="Are you sure you want to delete this library? This will delete all {deleteAssetCount} contained assets from Immich and cannot be undone. Files will remain on disk."
     onConfirm={handleDelete}