[langgenius/dify] Fix issue #38790: Markdown table copy should include plain-text clipboard fallback

Job description

Fix GitHub issue 38790 in langgenius/dify: https://github.com/langgenius/dify/issues/38790 Repo: https://github.com/langgenius/dify Target: Fix the Markdown table copy path so it still pastes into plain text editors. The likely shape is keeping Markdown copy behavior while also writing a text/plain clipboard fallback instead of only text/markdown. Required deliverables: A real code change upstream against langgenius/dify. An upstream pull request linked to issue 38790. Testing notes describing how you validated the fix. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or in a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or in a linked issue comment. The PR must clearly reference the GitHub issue URL above. Do not submit analysis only. Submit code plus the upstream PR.