Deliver final Harness answers to QQ as msg_type=2 markdown so bold,
headings, code blocks, lists, and tables render natively in QQ.
- add markdown-reply.mjs: chunk long answers at code-fence/table
boundaries (4500-char limit) and send each chunk with a unique
msg_seq to avoid passive-reply dedup (40054005)
- fall back to plain text per chunk when the platform rejects
markdown, so bots without markdown capability keep working
- route the non-stream final answer path in qq-bridge through the
markdown sender; streaming replies already use markdown content
type, and command/notice texts stay plain
