- Add jsdiff v7.0.0 via CDN for Myers diff algorithm
- Side-by-Side view: dual pane with synced scrolling, line numbers
- Unified view: single pane with dual line number columns
- Color coded: green=added, red=removed, white=same, striped=empty
- Summary stats bar: identical/added/removed counts + char counts
- View mode toggle: switch between side-by-side and unified
- Replace old raw text dump with real diff computation