Fix access denied screen to surface logged-out state as possible cause

[Copilot]

The "Access Denied" screen only showed "You must be an admin to view this page," which is misleading for users who are simply unauthenticated. This adds a second line of context so users know they may just be logged out.

Changes

• NotAuthorised component — adds optional additionalDescription?: string prop; renders a second EmptyStateDescription below the primary one when provided
• AdminClient.tsx — passes additionalDescription="You may also be logged out." to the NotAuthorised fallback in the admin RoleGuard
• NotAuthorised.stories.tsx — updates the Custom story to include additionalDescription

<NotAuthorised
  title="Access Denied"
  description="You must be an admin to view this page."
  additionalDescription="You may also be logged out."
/>

Type of change

• New feature or improvement (non-breaking change which adds/modifies functionality)

How Has This Been Tested?

• Manual testing (requires screenshots or videos)

Checklist before requesting a review

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added thorough tests that prove my fix is effective and that my feature works
• Additional issues have been created for any tech debt left in this PR
• I've requested a review from another user

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[FRONTEND] Fix access denied screen to let users know they could be logged out</issue_title>
<issue_description>Is your feature request related to a problem? Please describe.

Our "Access Denied" page is rather misleading as a user could just be logged out instead of "not being an admin". We should also add another quote stating the user could be logged out.

Additional context

BEFORE MERGING

• Storybooks created where possible
• Tested with react testing library
• Tests written for critical interactions
• PR Reviewed (For non-trivial changes)
• Changes tested after rebasing on master or merging in master (hint: git fetch origin master:master, then git rebase master or git merge master)
• All required PR checks passing
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [FRONTEND] Fix access denied screen to let users know they could be logged out #951

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[github-actions]

Preview Deployment Status

✅ Storybook Preview: https://ec5e0dc0.uabc-storybook.pages.dev

✅ Frontend Preview: https://ef340a99.uabc.pages.dev

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	76.75% (🎯 70%) ⬇️ -7.65%	1119 / 1458
🔵	Statements	76.59% (🎯 70%) ⬇️ -7.68%	1135 / 1482
🔵	Functions	64.45% (🎯 80%) ⬇️ -14.56%	194 / 301
🔵	Branches	69.46% (🎯 60%) ⬇️ -9.13%	448 / 645

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
apps/frontend/src/components/client/admin/AdminClient.tsx	0% 🟰 ±0%	100% 🟰 ±0%	0% 🟰 ±0%	0% 🟰 ±0%	14-34

Generated in workflow #3946 for commit 347b4ad by the Vitest Coverage Report Action