Rework modal header structure

src/app/components/EventInfo.svelte

@@ -14,6 +14,8 @@
   import Modal from "@lib/components/Modal.svelte"
   import ModalBody from "@lib/components/ModalBody.svelte"
   import ModalHeader from "@lib/components/ModalHeader.svelte"
+  import ModalTitle from "@lib/components/ModalTitle.svelte"
+  import ModalSubtitle from "@lib/components/ModalSubtitle.svelte"
   import {clip} from "@app/util/toast"
 
   type Props = {
@@ -41,12 +43,8 @@
 <Modal>
   <ModalBody>
     <ModalHeader>
-      {#snippet title()}
-        <div>Event Details</div>
-      {/snippet}
-      {#snippet info()}
-        <div>The full details of this event are shown below.</div>
-      {/snippet}
+      <ModalTitle>Event Details</ModalTitle>
+      <ModalSubtitle>The full details of this event are shown below.</ModalSubtitle>
     </ModalHeader>
     <FieldInline>
       {#snippet label()}