perf: cache editor layout geometry and preload styles to eliminate forced reflows

[ThisIs-Developer]

This Pull Request introduces elite performance and accessibility optimizations to resolve layout thrashing reflows and render-blocking styles.

Key Changes:

• Global Editor Geometry & Scroll Position Caching: Isolated and cached all layout values (cachedPaddingLeft, cachedPaddingRight, cachedLineHeight, etc.) in global variables, eliminating all DOM queries inside the updateLineNumbers() typing loop.
• High-Performance Asynchronous CSS Preloading: Replaced render-blocking tags for Bootstrap and GitHub-style Markdown CSS with preload tags and async onload handlers.
• Desktop App Synchronization: Programmatically parsed these preload tags and replaced them with offline local paths inside desktop-app/resources/.

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Project	Deployment	Actions	Updated (UTC)
markdown-viwer	Ready	Preview, Comment	May 31, 2026 3:43pm

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