chore(clean): remove dead CSS + normalize whitespace (tour CLN)

index.html: drop unused .reveal.d6 rule (markup uses d1-d5 only).

CV_Bastien_Chanot.html:
- remove dead `position: running(siteFooter)` — no `element()` consumer,
  and .footer-bar is `display:none` in @media print (the @page
  auto-numbered footer replaces it); on screen running() is an invalid
  position value, ignored.
- remove no-op `box-shadow: none` on .page (weasyprint ignores box-shadow;
  .page sets a shadow nowhere).
- remove dead `.skills-grid { font-size: 8.4pt }` (every direct child is a
  .skill-label/.skill-values div that sets its own size; no bare text).
- normalize stray blank lines.

Behavior-preserving: PDF regenerated from the edited HTML is byte-identical
to the pre-edit baseline (text sha256 + per-page PNG render hash match),
so CV_Bastien_Chanot.pdf is unchanged and the PDF=HTML invariant holds.

index.html

@@ -344,7 +344,6 @@
   .reveal.d3 { animation-delay: .30s; }
   .reveal.d4 { animation-delay: .42s; }
   .reveal.d5 { animation-delay: .55s; }
-  .reveal.d6 { animation-delay: .68s; }
   @keyframes rise {
     to { opacity: 1; transform: translateY(0); }
   }