Add Markdown Preview to FilePreview Component

[namanrajpal]

Feel free to comment and decline, just found it useful, hence opening a PR
Adds markdown rendering capability to the FilePreview component, allowing users to preview .md and .mdx files with proper syntax highlighting that respects the app's theme settings.

Features

• Markdown Preview Toggle: Preview rendered markdown or view raw source with a toggle button
• Theme-Aware Syntax Highlighting: Code blocks automatically adapt to light/dark/system theme
• GitHub Flavored Markdown: Full GFM support (tables, task lists, strikethrough, etc.)
• Large File Support: Works seamlessly with virtualized file viewing
• Clean Architecture: Reusable components following project conventions

Technical Changes

New Files

• MarkdownRenderer.tsx - Dedicated component for rendering markdown content
• MarkdownComponents.tsx - Shared ReactMarkdown component configurations

Modified Files

• FilePreview.tsx - Integrated markdown preview functionality
• index.css - Added theme-aware syntax highlighting styles

Dependencies Used

• react-markdown - Markdown to React conversion
• remark-gfm - GitHub Flavored Markdown support
• rehype-highlight - Syntax highlighting for code blocks
• rehype-raw - Support for raw HTML in markdown
• highlight.js - Syntax highlighting engine

📸 Preview

Users can now:

• Click the eye/code icon to toggle between rendered and raw markdown
• View code blocks with proper syntax highlighting
• See markdown that adapts to their theme preference (light/dark/system)

Testing Notes

• Test with .md and .mdx files
• Verify theme switching (Settings → Theme → Light/Dark/System)
• Check large markdown files with virtualization
• Confirm syntax highlighting in code blocks