fix(login): show error toast on sgID profile fetch non-401 errors

[Strikerprv]

Problem

SelectProfilePage unconditionally redirects all errors from useSgidProfiles to the login page with no user feedback. Only a 401 (unauthenticated) is a valid reason to redirect silently — all other errors (5xx, other 4xx, network failures) left users stuck in a silent redirect loop with no indication that the service was at fault.

Closes #9540

Solution

Gate the redirect on the error status code. Previously all errors redirected silently to /login with no feedback. Now all errors redirect to /login?status=<code>, leveraging the existing LoginPage status-based toast mechanism to surface a user-facing message appropriate to the error type:

• 401 → "Your session has expired, please log in again"
• 403 → "You are not authorised to access this page"
• 5xx → "A server error occurred. Please try again later."
• other → generic error message: "Something went wrong. Please try again later."

5xx range handling and the errors.serverError translation key were added to support the new explicit server error message.

Breaking Changes

• Yes - this PR contains breaking changes
• No - this PR is backwards compatible

Bug Fixes:

• SelectProfilePage: all errors now redirect to /login?status=<code> instead of silently redirecting to /login with no feedback, allowing LoginPage to surface the appropriate error toast per status code
• LoginPage: added 5xx range handling in the status-based toast switch — codes 500–599 now show 'A server error occurred. Please try again later.' instead of the generic fallback
• i18n: added errors.serverError translation key to features/common to support the explicit server error message

Before & After Screenshots

BEFORE:
User hits a 5xx on the sgID profiles endpoint → silently redirected to /login → re-attempts → infinite loop, no error shown

AFTER:
User hits a 500 → redirected to /login?status=500 → toast appears: 'A server error occurred. Please try again later.'

Tests

1. Override useSgidProfiles in queries.ts to throw Object.assign(new Error('Simulated 503'), { code: 503 })
2. Go through the sgID login flow
3. Confirm redirect lands on /login?status=503 with a server error toast visible
4. Change to { code: 401 } — confirm redirect lands on /login?status=401 with an expired session toast
5. Change to a plain new Error('network error') (no .code) — confirm redirect lands on /login?status=500 with a generic error toast
6. Revert queries.ts and confirm normal sgID login flow is unaffected

[Copilot]

Pull request overview

Improves the sgID login UX by ensuring sgID profile-fetch failures surface an error toast on the login page (instead of silently redirecting and potentially looping), and adds explicit messaging for 5xx server errors.

Changes:

• Update SelectProfilePage to redirect to /login?status=<code> for non-401 sgID profile fetch errors.
• Extend LoginPage’s status-to-toast mapping to treat 500–599 as a dedicated “server error” message.
• Add errors.serverError to the common i18n typings and en-sg locale.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
apps/frontend/src/i18n/locales/features/common/index.ts	Adds serverError key to the Common i18n type.
apps/frontend/src/i18n/locales/features/common/en-sg.ts	Adds the serverError message string in en-sg.
apps/frontend/src/features/login/SelectProfilePage.tsx	Redirects sgID profile-fetch errors to login with an attached status code (except 401).
apps/frontend/src/features/login/LoginPage.tsx	Adds 5xx-range handling to show a dedicated server-error toast.