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: position right-side label in margin zone (1.65cm x 23.42cm, right:-2.54cm)

fix: complete CSS rewrite - clean layout, no negative-margin tricks

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