fix(ui): forward-dialog header, notification presets, syntax-highlight tokens

- N14 ForwardMessageDialog: add folds <Header> with title + close IconButton
  (was closeable only by clicking outside)
- N20 Notification presets: bare <button> with undefined --border-interactive-
  normal / --bg-surface-low vars -> folds <Button variant="Secondary" fill="Soft">
- N68 syntaxHighlight tokenStyle: use the theme-aware --prism-* variable family
  (keyword/selector/boolean/atrule/comment) instead of TDS-only --lt-accent-*
  vars with dark-only Monokai fallbacks; comment uses --prism-comment not opacity

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/utils/syntaxHighlight.ts

@@ -306,19 +306,26 @@ export function tokenize(code: string, lang: string): SyntaxToken[] {
 
 // ── Inline style helpers ────────────────────────────────────────────────────
 
-/** Returns the React inline-style object for a given SyntaxToken type. */
+/**
+ * Returns the React inline-style object for a given SyntaxToken type.
+ *
+ * Uses the `--prism-*` variable family (defined in `ReactPrism.css`), which has
+ * proper light / dark / TDS palettes — unlike the raw `--lt-accent-*` vars,
+ * which only exist in TDS mode and otherwise fall back to dark-only Monokai
+ * colors with poor contrast on light themes.
+ */
 export function tokenStyle(type: SyntaxToken['type']): CSSProperties {
   switch (type) {
     case 'kw':
-      return { color: 'var(--lt-accent-cyan, #66d9ef)' };
+      return { color: 'var(--prism-keyword)' };
     case 'str':
-      return { color: 'var(--lt-accent-green, #a6e22e)' };
+      return { color: 'var(--prism-selector)' };
     case 'num':
-      return { color: 'var(--lt-accent-orange, #fd971f)' };
+      return { color: 'var(--prism-boolean)' };
     case 'cmt':
-      return { opacity: 0.5, fontStyle: 'italic' as const };
+      return { color: 'var(--prism-comment)', fontStyle: 'italic' as const };
     case 'fn':
-      return { color: 'var(--lt-accent-purple, #ae81ff)' };
+      return { color: 'var(--prism-atrule)' };
     default:
       return {};
   }