Add default 404 UI route handling with home navigation

[Copilot]

What is being addressed

The UI currently renders as if navigation succeeded even when the URL does not map to any page. This change introduces explicit not-found behavior so invalid routes surface a clear 404 state and a path back to the portal home.

How is this addressed

• Not-found presentation

  • Added NotFoundLayout to render a generic, themed 404 message and a home link (/), reusing existing Fluent UI patterns.

• Route fallback coverage

  • Added path="*" fallbacks in:
    • root layout routes
    • nested root sub-routes (/shared-services/*, /requests/*)
    • workspace provider nested routes
  • Unknown URLs now resolve to the 404 view instead of silently landing on unrelated content.

• Example of the routing change

  <Routes>
    {/* existing routes */}
    <Route path="*" element={<NotFoundLayout />} />
  </Routes>

• Documentation / template metadata

  • No docs, CHANGELOG.md, or template version updates are required for this UI behavior change.

[rudolphjacksonm]

@copilot update changelog to mention default 404 page on invalid url

[Copilot]

@copilot update changelog to mention default 404 page on invalid url

Updated in commit 231a374 by adding an Unreleased changelog entry for the default UI 404 page and home navigation on invalid URLs.