feat: add line numbers to code blocks with gutter styling
- Implemented line number display with absolute positioned gutter (40px width, right-aligned text)
- Added dynamic padding to pre element based on showLineNumbers state (3.5rem left padding when enabled)
- Moved hljs import to top-level for better performance and removed redundant dynamic imports
- Added ViewEncapsulation.None to enable global hljs theme styling
- Enhanced gutter styling with semi-transparent background, border, and pointer