fix #5479: navigate back to correct item path after deleting custom URL

[guillermo-escire]

References

Fixes #5479

Description

After deleting a custom URL (dspace.customurl) from an item via Administer, the "Back" button now correctly navigates to the item's UUID-based path instead of the deleted custom URL.

Instructions for Reviewers

List of changes in this PR:

• edit-item-page.component.ts: Updated getItemPage() to extract the UUID directly from the current edit URL instead of relying on item metadata, avoiding navigation to a potentially deleted custom URL.
• item-page.resolver.ts: Added a check to prevent the resolver from redirecting to the custom URL when navigating back from an edit/administer page.
• Updated specs for both files accordingly.

Steps to test:

1. Go to an item page that has dspace.customurl set
2. Click the three-dot menu → Administer
3. In the Metadata tab, delete the dspace.customurl field and click Save
4. Click Back
5. Verify that it navigates to the correct item page via UUID (not a 404)
6. Refresh the page and verify it stays on the correct item page

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