Bold+Strikethrough nested pattern (**~~text~~**) not working in browser automation

[drillan]

Description

When using browser automation (note_create_draft), nested markdown patterns like **~~text~~** do not render correctly. The bold markers remain as literal text instead of being converted to <strong> tags.

Current Behavior

Input: **~~text~~**
Result: **<s>text</s>** (literal ** text around strikethrough)

Expected Behavior

Input: **~~text~~**
Result: <strong><s>text</s></strong>

Root Cause

The _type_with_strikethrough() function in typing_helpers.py splits text by strikethrough pattern:

parts = _STRIKETHROUGH_PATTERN.split(text)  # "**~~text~~**" → ['**', 'text', '**']

This causes:

1. ** typed as normal text (not converted by ProseMirror)
2. ~~text~~ + SPACE triggers strikethrough conversion
3. ** typed as normal text

Workarounds

• Apply bold and strikethrough separately
• Manually apply bold in the browser editor after creation

Technical Notes

• This is NOT a ProseMirror limitation
• ProseMirror can handle nested patterns when typed correctly
• The issue is in how we split and process the text

Related

• Closes as part of strikethrough support (取り消し線（strikethrough）のMCP対応 #25) but nested patterns remain unsupported
• local markdown_to_html correctly handles nested patterns