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

---------

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

web/src/lib/components/shared-components/change-date.svelte

@@ -63,16 +63,16 @@
 
 <div role="presentation" on:keydown={handleKeydown}>
   <ConfirmDialogue
+    id="edit-date-time-modal"
     confirmColor="primary"
     cancelColor="secondary"
-    title="Edit date & time"
+    title="Edit date and time"
     prompt="Please select a new date:"
     disabled={!date.isValid}
     onConfirm={handleConfirm}
     onClose={handleCancel}
   >
     <div class="flex flex-col text-md px-4 text-center gap-2" slot="prompt">
-      <div class="mt-2" />
       <div class="flex flex-col">
         <label for="datetime">Date and Time</label>
         <DateInput