feat: add WebDAV journal storage support

src/modules/features/SetupWizard/dialogs/SetupRemote.svelte

@@ -10,6 +10,7 @@
         TYPE_COUCHDB,
         TYPE_BUCKET,
         TYPE_P2P,
+        TYPE_WEBDAV,
         TYPE_CANCELLED,
         type SetupRemoteResultType,
     } from "./setupDialogTypes";
@@ -26,12 +27,19 @@
             return "Continue to S3/MinIO/R2 setup";
         } else if (userType === TYPE_P2P) {
             return "Continue to Peer-to-Peer only setup";
+        } else if (userType === TYPE_WEBDAV) {
+            return "Continue to WebDAV setup";
         } else {
             return "Please select an option to proceed";
         }
     });
     const canProceed = $derived.by(() => {
-        return userType === TYPE_COUCHDB || userType === TYPE_BUCKET || userType === TYPE_P2P;
+        return (
+            userType === TYPE_COUCHDB ||
+            userType === TYPE_BUCKET ||
+            userType === TYPE_P2P ||
+            userType === TYPE_WEBDAV
+        );
     });
 </script>
 
@@ -46,6 +54,10 @@
         <Option selectedValue={TYPE_BUCKET} title="S3/MinIO/R2 Object Storage" bind:value={userType}>
             Synchronisation utilising journal files. You must have set up an S3/MinIO/R2 compatible object storage.
         </Option>
+        <Option selectedValue={TYPE_WEBDAV} title="WebDAV (Experimental)" bind:value={userType}>
+            Experimental synchronisation utilising journal files stored in a WebDAV collection. This is a proof of
+            concept for pluggable Journal storage backends.
+        </Option>
         <Option selectedValue={TYPE_P2P} title="Peer-to-Peer only" bind:value={userType}>
             This feature enables direct synchronisation between devices. No server is required, but both devices must be
             online at the same time for synchronisation to occur, and some features may be limited. Internet connection