When pad_tables=False (default), html2text generated table rows without
leading/trailing pipe delimiters, producing non-compliant GFM markdown:
Before: A | B | C
After: | A | B | C |
Changes:
- Add leading pipe on first cell, spaced pipe between cells
- Add trailing pipe at end of each row
- Format separator as | --- | --- | instead of ---|---
- Ensure table starts on its own line (soft_br at <table>)
- Handle <caption> element to prevent inline merge with header row
- All changes guarded by `not self.pad_tables` — pad_tables mode unchanged
Includes 13 unit tests covering GFM compliance and pad_tables regression.
Fixes: #1731
