feat: Add configurable backlinks placement and compact properties

[qtld88]

This PR adds two feature enhancements to improve layout flexibility and properties display :

Features Added

A. Configurable Backlinks Placement

• Toggle setting to place backlinks in footer (default) or right sidebar
• When in right sidebar: 1/3 height constraint with scrolling
• Appears below table of contents for logical flow
• Responsive design for mobile/tablet

B. Compact Frontmatter Properties

• Horizontal layout matching tags design
• Clickable URL detection for HTTP(S) links in property values
• Space-efficient display
• Type-aware styling (objects, arrays, primitives, null)
• Responsive design for all screen sizes

Technical Implementation

• New files: frontmatter-properties.ts (feature + component)
• Modified: backlinks.ts + multiple data structure files
• Updated: All translation files for multi-language support
• Added: Settings integration with proper feature toggles
• Includes: Responsive CSS and memory-efficient style injection