* fix: markdown table renders separator row as visible data
The alignment separator (|---|---|) at row index 1 was rendered as a
<td> row with dashes as cell content. Skip it and only open <tbody>
at that point, so tables render as header + data without the garbage
separator row in between.
* test: add regression test for table separator row rendering
Verifies that the markdown table renderer skips the separator row
(|---|---|) instead of rendering it as a visible data row. Also
updates the test harness to handle the splitTableRow import.
