implemented editing of document in GUI + respective handlers in backend

frontend/src/Components/MarkdownEditor.svelte

@@ -1,16 +1,20 @@
 <script>
     import { activeField } from './field_sync.svelte.js';
 
-    let { editable = false, value = $bindable(null) } = $props();
+    let { editable = false, value = $bindable(null), onSet = (newVal) => {} } = $props();
     let editing = $state(false);
 
     let editValue = $state({source:value.source,rendered:value.rendered});
 
     let timer = null;
-    function applyEdit(){
-        value.source = editValue.source;
-        value.rendered = editValue.rendered;
-        editing = false;
+
+    async function applyEdit(){
+        let success = await onSet(editValue.source);
+        if (success) {
+            value.source = editValue.source;
+            value.rendered = editValue.rendered;
+            editing = false;
+        } else resetEdit();
     }
 
     function resetEdit(){
@@ -54,12 +58,12 @@
         min-width: 40px;
         min-height: 20px;
     }
-    div:hover{
+    div.editable:hover{
         border: 1px dotted;
     }
 </style>
 
-{#if editable && editing}
+{#if editing}
 <textarea bind:value={editValue.source} onkeyup={typed} autofocus></textarea>
 {/if}
-<div onclick={startEdit}>{@html editValue.rendered}</div>
+<div onclick={startEdit} class={{editable}}>{@html editValue.rendered}</div>