fix(editor): use correct getMarkdown API for @tiptap/markdown (#217)

The migration from tiptap-markdown to @tiptap/markdown in 38e92040
broke comment creation. The old package stored getMarkdown() on
editor.storage.markdown, but the official @tiptap/markdown extension
adds it directly to the editor instance (editor.getMarkdown()).

This caused getEditorMarkdown() to always return "", making the
submit button permanently disabled and preventing any comments.

Also fix stale submitting ref in useIssueTimeline dependency array.

apps/web/components/common/rich-text-editor.tsx

@@ -203,10 +203,10 @@ const RichTextEditor = forwardRef<RichTextEditorRef, RichTextEditorProps>(
     const onUpdateRef = useRef(onUpdate);
     const onSubmitRef = useRef(onSubmit);
 
-    // Helper to get markdown from tiptap-markdown storage
+    // Helper to get markdown from @tiptap/markdown extension
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     const getEditorMarkdown = (ed: any): string =>
-      ed?.storage?.markdown?.getMarkdown?.() ?? "";
+      ed?.getMarkdown?.() ?? "";
 
     // Keep refs in sync without recreating editor
     onUpdateRef.current = onUpdate;

apps/web/features/issues/hooks/use-issue-timeline.ts

@@ -202,7 +202,7 @@ export function useIssueTimeline(issueId: string, userId?: string) {
         setSubmitting(false);
       }
     },
-    [issueId, userId, submitting],
+    [issueId, userId],
   );
 
   const submitReply = useCallback(