text: Title: [FEATURE] Create a New Topbar Component
  Body: #### **Overview**
  
  The **default top bar** in every Preswald app is currently **hardcoded** inside `preswald/frontend/layout/`. This should be refactored into a **separate Preswald component**.
  
  ### Adding a new component 
  
  https://docs.preswald.com/addnewcomponent 
  
  #### **Changes Required**
  
  1. **Move existing top bar code** from default layout into its own widget kind of like other components like selectbox
  2. **Expose `topbar` as a Preswald component** that users can explicitly include:
      
      ```python
      from preswald import topbar
      topbar()
      ```
      
  3. **Remove the sidebar toggle button** from the top bar (since it is now in the sidebar).
  4. **Ensure default behavior remains unchanged** for apps that do not include `topbar()` explicitly.
  
  #### **Testing**
  
  -  Create a sample preswald app using `preswald init` and include and don't include the topbar() and make sure it all works 
  
  #### **Update Documentation**
  
  - Add `topbar` documentation to `docs/sdk/topbar.md`, including examples and screenshots.
  - Update `preswald/tutorial` with an example of how to use the `topbar` component.
  - Run `preswald tutorial` and verify that the top bar is included only when explicitly added.
  