chore(clean): enforce palette + reduced-motion, drop dead CSS

- 5x background:#fff -> var(--page) (stack/project/theme/methode cards +
  CV body) per CLAUDE.md 'no pure white background' (user-approved strict
  conformity; visual change: cards now blend with parchment, border-kept)
- prefers-reduced-motion now also kills transitions (universal rule)
- dead .screen-label rule removed (no matching element)
- PDF regenerated via weasyprint (must match HTML invariant)

CV_Bastien_Chanot.html

@@ -37,7 +37,7 @@
   * { margin: 0; padding: 0; box-sizing: border-box; }
 
   body {
-    background: #fff;
+    background: var(--page);
     font-family: var(--sans);
     -webkit-font-smoothing: antialiased;
     margin: 0;
@@ -435,7 +435,6 @@
         linear-gradient(160deg, #f5f3ec 0%, #edeadf 55%, #f2efe6 100%);
       padding: 0;
     }
-    .screen-label { display: none; }
     .page { box-shadow: none; background: transparent; }
     .cv-header { padding: 18px 14mm 14px; }
     .cv-body { padding: 10px 14mm 12px; background: transparent; }