Fix doc panel images (#10673)

Transformers from our custom plugins were ignored because of misconfiguration of lexical markdown plugin.

Part of #10435


https://github.com/user-attachments/assets/48b22546-9893-42f8-9a3b-5ed6070c4eaf

app/gui2/src/components/MarkdownEditor/ImagePlugin/LexicalImage.vue

@@ -30,6 +30,8 @@ const title = computed(() =>
   : '',
 )
 
+const alt = props.alt ? props.alt : DEFAULT_ALT_TEXT
+
 onUnmounted(() => {
   if (data.value?.ok) data.value.value.dispose?.()
 })

app/gui2/src/components/MarkdownEditor/markdown.ts

@@ -28,27 +28,29 @@ export function markdownPlugin(
     if (extension?.transformers) transformers.push(...extension.transformers)
   }
   transformers.push(...TRANSFORMERS)
-  return [...extensions, baseMarkdownPlugin, markdownSyncPlugin(model, transformers)]
+  return [...extensions, baseMarkdownPlugin(transformers), markdownSyncPlugin(model, transformers)]
 }
 
-const baseMarkdownPlugin: LexicalPlugin = {
-  nodes: [
-    HeadingNode,
-    QuoteNode,
-    ListItemNode,
-    ListNode,
-    AutoLinkNode,
-    LinkNode,
-    CodeHighlightNode,
-    CodeNode,
-    TableCellNode,
-    TableNode,
-    TableRowNode,
-  ],
-  register: (editor) => {
-    registerRichText(editor)
-    registerMarkdownShortcuts(editor, TRANSFORMERS)
-  },
+function baseMarkdownPlugin(transformers: Transformer[]): LexicalPlugin {
+  return {
+    nodes: [
+      HeadingNode,
+      QuoteNode,
+      ListItemNode,
+      ListNode,
+      AutoLinkNode,
+      LinkNode,
+      CodeHighlightNode,
+      CodeNode,
+      TableCellNode,
+      TableNode,
+      TableRowNode,
+    ],
+    register: (editor) => {
+      registerRichText(editor)
+      registerMarkdownShortcuts(editor, transformers)
+    },
+  }
 }
 
 const markdownSyncPlugin = (model: Ref<string>, transformers: Transformer[]): LexicalPlugin => ({