audit: enforce design rules and enhance handbook formatting

fix: layout refinements + update deps

feat: overlay-based header+label on content pages only (pypdf merge)

fix: label at right:0 inside content area with padding-right, add debug log

feat: right-side label on content pages only (pages 3+, excludes cover/fullpage)

fix: ISP handbook styling overhaul - margins, typography, emphasis, benefits, CSS cascade