Tabox v4.1: full-page workspace, drag-and-drop upgrades, and sync reliability improvements

[gil-wix]

Summary

This PR delivers the main v4.1 workstream across the popup, full-page experience, drag-and-drop flows, storage/migration logic, and sync behavior.

What’s included

• Adds a new full-page Tabox experience with dedicated layout, cards, panels, sidebar, top bar, and related interactions
• Introduces command palette and multi-select UI building blocks
• Expands drag-and-drop support for collections, folders, groups, and tab rows
• Improves collection and folder operations across the main UI
• Updates storage, migration, backup, validation, and shared utility logic
• Strengthens background sync/session handling and related background helpers
• Adds broad automated test coverage for new UI flows, drag behavior, sync scenarios, migrations, and full-page functionality
• Updates repo ignore rules so local tool folders and API key files are not tracked by git