Fix braindump display and switching issues

- Add echo API endpoint for Echo component
- Export Echo component from ui crate to fix compilation errors
- Fix notes not showing after save by adding refresh_notes callback that updates the notes resource
- Fix note content not updating when switching notes by using reactive signal for note_id which triggers note resource reload on prop changes

💘 Generated with Crush

packages/ui/src/lib.rs

@@ -1,7 +1,10 @@
-//! This crate contains all shared UI for the workspace.
+//! This is the UI package for the braindump application.
 
 mod hero;
 pub use hero::Hero;
 
 mod navbar;
 pub use navbar::Navbar;
+
+mod echo;
+pub use echo::Echo;