M3: dead code purge + layer refs → semantic tokens

Dead code removed:
- 05-utilities: grid-2/card-grid/stats block (superseded by 08-layout)
- 02-semantic: dialog min-width:100% (conflicted with 03-components)
- 02-semantic: hgroup p dead font-family, redundant nested list margin
- All layers: [ai-disclosure] → [data-ai-disclosure] (bug fix)
- table.striped → [data-table="striped"] (classless alignment)

Ref cleanup: 12 --gray-N/--green-N/--blue-N replaced with semantic
tokens. 24 refs marked TODO (syntax highlighting needs --syntax-* aliases).

assets/css/layers/08-layout.css

@@ -31,6 +31,7 @@ body {
 
 /* ── Hero ──────────────────────────────────────────────────────────── */
 /* Landing page hero block. Usually <header data-layout="hero">. */
+/* Base hero — 09-landing.css overrides for full landing pages */
 [data-layout="hero"] {
   text-align: center;
   padding: var(--space-8) var(--space-5);
@@ -541,8 +542,8 @@ main[data-layout="prose"],
 /* Print styles */
 @media print {
   [data-layout="report"] {
-    --surface: var(--gray-0);
-    --text: var(--gray-15);
+    --surface: var(--gray-0);   /* TODO: map to semantic token — overriding --surface for print; no alias for gray-0 as "print-white" */
+    --text: var(--gray-15);     /* TODO: map to semantic token — overriding --text for print; no alias for gray-15 as "print-black" */
     font-size: 11pt;
   }