fix(ui): escape brackets in filename and use paragraph break for inline images

Escape `[` and `]` in filenames to prevent malformed markdown when
attaching images. Use `\n\n` instead of `\n` so the image renders
as its own paragraph instead of inline with preceding text.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/CommentThread.tsx

@@ -340,8 +340,9 @@ export function CommentThread({
     try {
       if (imageUploadHandler) {
         const url = await imageUploadHandler(file);
-        const markdown = `![${file.name}](${url})`;
-        setBody((prev) => prev ? `${prev}\n${markdown}` : markdown);
+        const safeName = file.name.replace(/[[\]]/g, "\\$&");
+        const markdown = `![${safeName}](${url})`;
+        setBody((prev) => prev ? `${prev}\n\n${markdown}` : markdown);
       } else if (onAttachImage) {
         await onAttachImage(file);
       }