Add responsive video embed styling and improve iframe base URL handling

[NateEaton]

Summary

This PR enhances video content handling by adding responsive video embed styling across all HTML templates and improving how iframe base URLs are extracted for proper content loading.

Key Changes

• Added responsive video embed CSS to all three HTML templates (dark, light, sepia):

  • New .video-embed class using padding-bottom technique for 16:9 aspect ratio
  • Absolute positioning for iframe and video elements to maintain responsiveness
  • Consistent margins matching other content blocks

• Improved iframe base URL extraction in BookmarkDetailScreen:

  • New extractEmbedBaseUrl() function that parses iframe src attributes using regex
  • Safely extracts scheme and host from embed HTML for use as WebView base URL
  • Graceful fallback to original bookmark URL if parsing fails

• Enhanced video embed HTML wrapping in BookmarkDetailViewModel:

  • Automatically wraps iframe embeds in the new .video-embed div container
  • Preserves non-iframe embed content as-is
  • Ensures proper responsive behavior for embedded videos

Implementation Details

• The extractEmbedBaseUrl() function uses regex to find iframe src attributes and Uri.parse() for safe URL parsing
• The responsive video technique uses padding-top: 56.25% to maintain 16:9 aspect ratio without knowing video dimensions
• Changes are applied consistently across all theme variants to maintain visual consistency

https://claude.ai/code/session_01KfcuMiGfVnvJu14WGLK6yR

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