feat: add file block with drag-and-drop support
- Implemented file upload block with preview support for images, videos, PDFs, text, code, and DOCX files
- Added drag-and-drop directive for files with visual drop indicators in root and column contexts
- Created file icon component with FontAwesome integration for 50+ file type icons
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- Added clickable app title links in header and sidebar that reset view to all markdown files
- Fixed quicklink filtering to use correct frontmatter boolean keys (favoris, publish, draft, etc.)
- Updated sidebar behavior to auto-open Quick Links section when viewing markdown files
- Added filter clearing when switching between views to prevent conflicting filters
- Modified URL state handling to preserve kind parameter when navigating
- Enforced markdown-only
