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/api/src/lib.rs

@@ -113,3 +113,8 @@ pub async fn toggle_pin_note(id: String) -> Result<(), ServerFnError> {
         Err(ServerFnError::new("Note not found".to_string()))
     }
 }
+
+#[post("/api/echo")]
+pub async fn echo(message: String) -> Result<String, ServerFnError> {
+    Ok(format!("Echo: {}", message))
+}