fix(cn): use canonical twMerge(clsx) so class overrides resolve

The local cn() joined classes with filter(Boolean).join(' '), which doesn't
dedupe conflicting Tailwind utilities — consumer className overrides could
silently lose to the component's base classes. Switch to the standard
twMerge(clsx(...)) (clsx + tailwind-merge are already app deps). Behaviour is
unchanged except conflicting overrides now win correctly. Build-verified
(skyai-finance clean; vibespace transforms all modules). Frontend audit rank 4.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/index.tsx

@@ -1,3 +1,5 @@
+import { clsx } from "clsx"
+import { twMerge } from "tailwind-merge"
 // PURPOSE: Personal-records primitives — kind-typed record cards, group
 //          sections with privacy framing, field tables and spec-driven
 //          field inputs, tier badges, the record→Markdown renderer, and a
@@ -47,7 +49,7 @@ import {
 /* ------------------------------------------------------------------ */
 
 function cn(...classes: (string | false | null | undefined)[]): string {
-  return classes.filter(Boolean).join(" ");
+  return twMerge(clsx(classes))
 }
 
 /* ------------------------------------------------------------------ */