ROOT CAUSE:
When saving card edit in EmailBuilder, htmlToMarkdown() was called.
The old code at line 26 converted ALL <a> tags to markdown links:
<a href="url">text</a> → [text](url)
This lost TipTap button data-button attributes, converting buttons
to plain text instead of [button:style](url)Text[/button] shortcode.
FIX:
Added TipTap button detection BEFORE generic link conversion in
html-to-markdown.ts:
- Detects <a data-button...> elements
- Extracts style from data-style or class attribute
- Extracts URL from data-href or href attribute
- Converts to [button:style](url)Text[/button] format
FLOW NOW WORKS:
1. User adds button via TipTap toolbar
2. TipTap renders <a data-button data-style="solid"...>
3. User clicks Save Changes
4. htmlToMarkdown detects data-button → [button:solid](url)Text[/button]
5. Card content saved with proper button shortcode
6. On re-edit, button shortcode converted back to TipTap button
