fix(ui): readable date-time trigger, showcase code panel, release ui 0.8.88

- DatePicker trigger shows the value formatted in the component locale
  ("Oct 2, 2026 · 9:30 AM", "Jul 15, 2026"); the hidden input still submits
  the ISO value.
- Showcase playground code panel: the reactive runtime read "{...}" in the
  rewritten code as interpolations and blanked every object in array props.
  Braces are now written as their own spans, like the server-rendered code.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

bun.lock

@@ -749,7 +749,7 @@
     },
     "packages/ui": {
       "name": "@wrnexus/ui",
-      "version": "0.8.87",
+      "version": "0.8.88",
       "dependencies": {
         "@wrnexus/core": "workspace:*",
       },