Fix UIResource \_meta type to match actual usage pattern

The UIResource interface incorrectly specified `_meta?: UIResourceMeta`
when it should be `_meta?: { ui?: UiResourceMeta }` to match the
resources/read response format and all usage examples throughout the
document.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: jonathanhefner

specification/draft/apps.mdx

@@ -101,7 +101,9 @@ interface UIResource {
    * Includes Content Security Policy configuration, dedicated domain settings,
    * and visual preferences.
    */
-  _meta?: UIResourceMeta
+  _meta?: {
+    ui?: UiResourceMeta;
+  }
 }
 
 interface UIResourceMeta {