fix: preserve Feishu markdown around tables

[xue2han]

Summary

• convert outbound Markdown table blocks to fenced text code blocks for Feishu posts
• keep the rest of the message rendered as rich Markdown instead of downgrading the whole reply to plain text
• add Feishu outbound payload regression tests

Test Plan

• python -m pytest tests/gateway/test_feishu.py -k 'markdown_table_reply_stays_rich_post or plain_text_reply_remains_text_message' -q -o 'addopts='
• python -m pytest tests/gateway/test_feishu.py -q -o 'addopts='
• manual payload check: table reply now emits msg_type=post with table block fenced as ```text

[alt-glitch]

Duplicate of #21872 — same code-fence approach to Feishu markdown table rendering (convert tables to fenced text, keep rest as rich post) within the saturated Feishu table cluster (#22259, #27469). Note: this PR's diff also carries unrelated stacked-branch changes (agent/codex_*, cron/scheduler.py, cli.py, gateway/config.py, a tinker-atropos submodule) — the actual fix is gateway/platforms/feishu.py only.

[xue2han]

Closing per request.