Refactor web app code and add background color setting

web-app/src/lib/components/MarkdownEditor.svelte

@@ -0,0 +1,72 @@
+<script lang="ts">
+  import { deserialize, applyAction } from "$app/forms";
+  import { textareaScrollTop, previewContent } from "$lib/runes.svelte";
+
+  const {
+    apiPrefix,
+    label,
+    name,
+    content
+  }: { apiPrefix: string; label: string; name: string; content: string } = $props();
+
+  let mainContentTextarea: HTMLTextAreaElement;
+
+  const updateScrollPercentage = () => {
+    const { scrollTop, scrollHeight, clientHeight } = mainContentTextarea;
+    textareaScrollTop.value = (scrollTop / (scrollHeight - clientHeight)) * 100;
+  };
+
+  const handleImagePaste = async (event: ClipboardEvent) => {
+    const clipboardItems = Array.from(event.clipboardData?.items ?? []);
+    const file = clipboardItems.find((item) => item.type.startsWith("image/"));
+
+    if (!file) return null;
+
+    event.preventDefault();
+
+    const fileObject = file.getAsFile();
+
+    if (!fileObject) return;
+
+    const formData = new FormData();
+    formData.append("file", fileObject);
+
+    const request = await fetch("?/pasteImage", {
+      method: "POST",
+      body: formData
+    });
+
+    const result = deserialize(await request.clone().text());
+    applyAction(result);
+
+    const response = await request.json();
+
+    if (JSON.parse(response.data)[1]) {
+      const fileId = JSON.parse(response.data)[4];
+      const fileUrl = `${apiPrefix}/rpc/retrieve_file?id=${fileId}`;
+
+      const target = event.target as HTMLTextAreaElement;
+      const newContent =
+        target.value.slice(0, target.selectionStart) +
+        `![](${fileUrl})` +
+        target.value.slice(target.selectionStart);
+
+      previewContent.value = newContent;
+    } else {
+      return;
+    }
+  };
+</script>
+
+<label>
+  {label}:
+  <textarea
+    {name}
+    rows="20"
+    bind:value={previewContent.value}
+    bind:this={mainContentTextarea}
+    onscroll={updateScrollPercentage}
+    onpaste={handleImagePaste}
+    required>{content}</textarea
+  >
+</label>