feat: add collapsible block type and enhance paragraph menu UX
- Added CollapsibleBlockComponent with registration in block host and columns
- Enhanced paragraph block with inline "+" button for column layouts and improved menu positioning
- Updated toggle block to support creating new toggle blocks below with dedicated event handlers
- Improved menu styling with fixed positioning, keyboard navigation (arrows, Enter, Escape), and focus management
- Simplified inline action handling by deleg
- Added timestamp, author, and description fields to both compact and detailed view modes
- Implemented thumbnail support in detailed view with automatic image extraction from note content
- Improved auto-selection behavior when filters change using reactive signals for more reliable note navigation
- Implemented multi-selection for notes with Ctrl+click, long-press, and keyboard shortcuts (Ctrl+A, Escape)
- Added Gemini API integration with environment configuration and routes
- Enhanced code block UI with improved copy feedback animation and visual polish
- Added sort order toggle (asc/desc) for note lists with persistent state
