Update Passbolt guide for version 5

[AminZoubaa]

Summary

• update the Passbolt guide to use PHP 8.3 and Composer 2
• add an Uberspace-specific update flow for source installations, including backups, release tags, migrations, cleanup dry-run and config comparison
• document the RewriteBase / requirement for additional DocumentRoots to avoid Apache internal redirect loops / HTTP 500 after updating
• refresh the tested version information for Passbolt 5.11.0

Verification

• python check-guides.py --check --warn source/guide_passbolt.rst passes for this guide
• full make check-guides still reports pre-existing issues in unrelated guides
• full Sphinx build could not run locally because the system enchant C library required by sphinxcontrib.spelling is missing