Rework modal header structure

src/app/components/SpaceEdit.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 ModalFooter from "@lib/components/ModalFooter.svelte"
   import ImageIcon from "@lib/components/ImageIcon.svelte"
   import IconPickerButton from "@lib/components/IconPickerButton.svelte"
@@ -124,12 +126,8 @@
 <Modal tag="form" onsubmit={preventDefault(trySubmit)}>
   <ModalBody>
     <ModalHeader>
-      {#snippet title()}
-        <div>Edit a Space</div>
-      {/snippet}
-      {#snippet info()}
-        <span class="text-primary">{displayRelayUrl(url)}</span>
-      {/snippet}
+      <ModalTitle>Edit a Space</ModalTitle>
+      <ModalSubtitle><span class="text-primary">{displayRelayUrl(url)}</span></ModalSubtitle>
     </ModalHeader>
     <FieldInline>
       {#snippet label()}