fix: ensure full-height layout

[wgu-jesse-stewart]

Fixes openedx/frontend-app-learning#1695
Related PR: openedx/frontend-lib-special-exams#164, openedx/frontend-app-learning#1724

This PR simply adds a app-container div or easy styling of app wrapping component

Summary:
When content within a sequence is shorter than the height of the browser viewport, the .sequence-container > .outline-sidebar-wrapper element does not expand appropriately. This causes the course outline sidebar to be partially or completely hidden from view.

Steps to Reproduce:

Open a course sequence that contains very little content (e.g., a short paragraph or notice).

View the course in a tall browser window.

Observe that the sidebar navigation is cut off or hidden.

Expected Behavior:
The sidebar should remain fully visible and accessible, regardless of the amount of content in the main pane.

Actual Behavior:
When the content is short, the parent container height collapses to fit that content, which in turn restricts the sidebar’s height, hiding part of the navigation.

Screenshots:

Demo of fix:
https://github.com/user-attachments/assets/69ce8dae-e73b-487c-bc6a-862701b1ce8d

I think we should have a discussion about removing these wrapper divs entirely so that the layout can handle all the UI

Merge checklist:

• Consider running your code modifications in the included example app within frontend-platform. This can be done by running npm start and opening http://localhost:8080.
• Consider testing your code modifications in another local micro-frontend using local aliases configured via the module.config.js file in frontend-build.
• Verify your commit title/body conforms to the conventional commits format (e.g., fix, feat) and is appropriate for your code change. Consider whether your code is a breaking change, and modify your commit accordingly.

Post merge:

• After the build finishes for the merged commit, verify the new release has been pushed to NPM.

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.79%. Comparing base (93bee06) to head (2c9f2d4).
Report is 1 commits behind head on master.

Additional details and impacted files

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  Coverage   86.79%   86.79%           
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  Files          48       48           
  Lines        1401     1401           
  Branches      297      294    -3     
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  Hits         1216     1216           
  Misses        172      172           
  Partials       13       13           

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Pull Request Overview

This PR addresses the issue of a collapsing sidebar when the main content is short by adding a classname for easier styling of the browser router container.

• Adds the "browser-router" classname to the container div within the Router.
• Aims to ensure the sidebar remains fully visible with a full-height layout.

Comments suppressed due to low confidence (1)

src/react/AppProvider.jsx:102

• [nitpick] Consider adding an inline comment to clarify that the 'browser-router' class is added solely to support the full-height layout for the sidebar. This can aid future developers in understanding the rationale behind this styling hook.

<div className="browser-router" data-testid="browser-router">

[arbrandes]

Not that I'm fundamentally opposed to having a generic class name such as this one, here, but I'm hesitant to introduce a layout feature to what is essentially a data div. Can the desired outcome not be achieved by styling #main-content or SidebarProviderComponent instead?

[brian-smith-tcril]

I think we probably just shouldn't have that extra div in there at all. It looks like it was added purely for testing purposes in #615

Edit: tried removing the div and got the tests to pass again by mocking the router in the test file

jest.mock('react-router-dom', () => ({
  BrowserRouter: ({children}) => (
    <div data-testid="browser-router">
      {children}
    </div>
  ),
}))

[wgu-jesse-stewart]

I think this is great feedback - I will close this PR and deprecate that test id property in another PR