fix(feishu): send markdown tables as post format instead of plain text

[haozicnm]

Feishu post-type 'md' elements now support markdown tables (verified with v1.0.39 on 2026-05-24).

The method had an outdated check that forced all content containing markdown tables to format (plain text), making formatted messages unreadable on the Feishu client.

Change: Merge the check into the branch so tables also go through the format path.

Before:

• Tables → forced plain text (raw markdown visible)
• Bold/lists/code → post format (renders correctly)

After:

• Tables → post format (renders correctly)
• Bold/lists/code → post format (unchanged)

[alt-glitch]

This is part of the Feishu markdown table rendering duplicate cluster tracked by meta-issue #27469. Root issue: #9549. Competing PRs include #31056, #29510, #29552, #27739, #16194, #12114, and others.

Please coordinate with existing PRs before proceeding.