fix(agents): correct state layer count from three to four in ui-development.md

Signed-off-by: StreamKit Devin <devin@streamkit.dev>
Co-Authored-By: Claudio Costa <cstcld91@gmail.com>

Author: streamkit-devin

agent_docs/ui-development.md

@@ -11,7 +11,7 @@ and Bun.
 
 ## State Management
 
-StreamKit uses three complementary state layers:
+StreamKit uses four complementary state layers:
 
 | Layer | Tool | Purpose |
 |-------|------|---------|