feat(app): add transparent Open in icon toggle

[edoedac0]

Summary

• add a new Appearance setting to control whether Open in app icons render as transparent logos without the default framed background
• apply the setting to the session header Open in button and app picker so users can switch between the new transparent look (default on) and the previous framed style
• update the Cursor app icon asset to the new logo provided by design

Notes

• this keeps Open in app desktop-only behavior unchanged
• commit: 64904d827

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