Fixed editor losing formatting on save

Saving a post would sometimes strip formatting — particularly nested lists and code blocks.

Root cause

The markdown conversion step (HTML → Markdown → HTML roundtrip) was using a regex-based approach that couldn't handle:

• Nested <ul> inside <ol> (and vice versa)

• Code blocks containing HTML-like syntax

• Blockquotes with multiple paragraphs

The fix

We replaced the regex-based converter with a proper AST-based serializer that correctly handles all TipTap node types.

All formatting is now preserved through save and reload cycles — including edge cases like:

• Nested lists 3+ levels deep

• Code blocks with <script> tags inside

• Blockquotes containing lists and code

If you had posts with broken formatting, re-editing and saving them will now preserve the correct structure.