Markdown parser replaced with goldmark (GFM extension) for robust AST-based rendering

Table columns are now aligned with computed max-width padding

Markdown viewer: mouse wheel scrolling

Markdown viewer: key repeat on j/k and arrow keys for continuous scrolling

Markdown viewer: vim motions — gg (top), G (bottom), Ctrl+d (half-page down), Ctrl+u (half-page up)

Markdown viewer: strikethrough, image, task list checkbox, and table rendering styles

Markdown viewer close leaving grey screen — added ClearPaneCache on dismiss

Markdown viewer content capture uses full block output range instead of visible viewport