fix(feishu): convert markdown tables to lists before rendering

[thunderredondo]

Problem

Feishu's md renderer (used in post messages) does not support markdown table syntax. When a message contains | col | col | tables, they render as blank cells. In some cases the blank table also swallows trailing content.

This is a known limitation of Feishu's post message format — the md tag spec omits table support entirely. It's not a transient rendering glitch.

Reproduction

Send any markdown table via the Feishu post API:

{"tag": "md", "text": "| A | B |\n|---|---|\n| 1 | 2 |"}

Result: blank space where the table should be.

Fix

Add _convert_tables_to_text() to gateway/platforms/feishu.py which:

1. Detects markdown table blocks (header row + separator row + data rows)
2. Converts each data row to a bullet list item using header values as labels
3. Leaves pipes inside fenced code blocks untouched

The conversion runs at the top of _build_markdown_post_rows(), so all outbound Feishu markdown messages benefit automatically.

Before (blank)

| 项目 | 值 | 说明 |
|------|-----|------|
| 模型 | mimo-v2.5-pro | 主模型 |

After (readable)

- 项目：模型 | 值：mimo-v2.5-pro | 说明：主模型

Tests

9 unit tests covering:

• Simple 2-column and 3-column tables
• Table with surrounding prose
• No-table content passthrough
• Pipe inside code block not treated as table
• Empty cells
• Single row table
• Integration with _build_markdown_post_rows

All 194 existing Feishu tests pass with zero regressions.

[alt-glitch]

Duplicate of #15956 — same fix approach (convert markdown tables to text/lists for Feishu post messages). Also competes with #20028 and addresses #9549.

[thunderredondo]

Closing as duplicate of #15956 (same approach, 10 days earlier). Hoping #15956 or #20028 gets merged soon — the Feishu table rendering issue is a real pain point.

Thanks @alt-glitch for pointing it out.