feat: set pasting image default folder & resolve macOS screenshot scale & setting shortcut

[maxrks]

Summary

This PR implements three user-requested features to improve the image handling and accessibility of Markpad.

Features Implemented

1. Image Directory Configuration

• Added setting to allow users to configure the target directory name for pasted images
• Defaults to "img" but can be changed to any directory name
• The setting is persisted in localStorage

2. macOS Image Scaling Toggle

• Added toggle option to enable/disable automatic 50% scaling for macOS screenshots
• Uses high-quality Lanczos3 filter for optimal image clarity
• The setting is only visible on macOS platform

3. Settings Keyboard Shortcut

• Added keyboard shortcut to open settings:
  • macOS: cmd+,
  • Windows: ctrl+,
• Works globally across the application

Files Modified

• src/lib/stores/settings.svelte.ts - Added image directory and macOS scaling settings
• src/lib/components/Settings.svelte - Added new setting options in UI
• src/lib/components/Editor.svelte - Updated to use configured image directory
• src-tauri/src/lib.rs - Modified image handling functions to support directory configuration and scaling
• src/lib/MarkdownViewer.svelte - Added keyboard shortcut handling

Impact

• User Experience: Provides more control over image handling and quick access to settings
• Compatibility: Maintains cross-platform support
• Performance: Minimal impact, scaling only occurs on macOS when enabled
• Accessibility: Improves keyboard navigation with new shortcut

Testing

• Verified image directory setting works correctly
• Confirmed macOS scaling toggle functions as expected
• Tested keyboard shortcut on both macOS and Windows
• Ensured all changes compile and run without errors