fix(feishu): try post-type before falling back to text for markdown tables

[wydty]

Problem

_build_outbound_payload() pre-emptively forces text message type for any
content containing markdown tables, even when other markdown (bold, code,
lists) is also present. This sacrifices all formatting just because the
message happens to contain a table.

Feishu's post message type with md tag does support table rendering
on most clients, though behavior varies by client version.

Solution

Remove the pre-emptive table detection from _build_outbound_payload, letting
tables flow through the normal markdown detection logic:

• Tables + other markdown (bold, code, etc.) → post type → md tag
  → Feishu renders the table on capable clients
• Tables only (no other markdown) → text type (unchanged from before)
• If Feishu API rejects the post payload → existing fallback in
  _send_message_chunks degrades to plain text automatically

The _MARKDOWN_TABLE_RE regex is retained as documentation but no longer
drives payload construction.

Tests

All 397 existing feishu-related tests pass.

[teknium1]

Thanks for the focused table-rendering proposal. The underlying routing problem is still present on current main: plugins/platforms/feishu/adapter.py:4524-4534 returns text before evaluating _MARKDOWN_HINT_RE when _MARKDOWN_TABLE_RE matches.

Problems

• The PR modifies the former gateway/platforms/feishu.py, but 560010547 moved the active adapter to plugins/platforms/feishu/adapter.py; the PR currently conflicts.
• The stale diff also removes webhook authentication/config handling and approval-click authorization. Current main enforces approval state, operator authorization, and chat binding at plugins/platforms/feishu/adapter.py:2706-2744; those changes must not be included in a table-routing fix.
• No table-routing regression test is added. Existing fallback coverage at tests/gateway/test_feishu.py:529-569 is generic and does not assert the table-plus-markdown decision.

Suggested changes

• Salvage only the payload-routing change into plugins/platforms/feishu/adapter.py:_build_outbound_payload().
• Add focused routing tests for a table combined with another markdown hint, plus the intended table-only behavior.

This is an automated hermes-sweeper review.