[Bookmarks] Import bookmarks directly from installed browsers

[shadowbipnode]

Add direct bookmark import from locally installed browsers.

Goals:

• detect installed browsers/profiles where possible
• support importing from:
  • Brave
  • Chrome / Chromium
  • Firefox
  • Edge
• support Linux first, then Windows/macOS
• preserve folders where possible
• avoid duplicates when importing multiple times
• show preview/count before import
• keep HTML import/export as fallback path

Notes:
This is different from HTML bookmark import/export. This feature should read browser profile bookmark files directly when available.

Potential paths:

• Chromium/Brave/Chrome: profile Bookmarks JSON
• Firefox: places.sqlite bookmarks
• Linux paths first:
  • ~/.config/BraveSoftware/Brave-Browser/
  • ~/.config/google-chrome/
  • ~/.config/chromium/
  • ~/.mozilla/firefox/

Security/privacy:

• read-only import
• no browser profile modification
• clear user confirmation before importing.