fix: restore unauthenticated space switching

[alexk-dev]

What changed

• Moves the image version marker out of the header and into the bottom of the sidebar.
• Adds a standalone adaptive space switcher for sessions without an account menu.
• Keeps the authenticated space switcher inside the existing user menu unchanged.
• Reloads the visible viewer page when the active space changes, including the same / route.
• Covers the standalone switcher and sidebar version placement with tests.

Why

When authentication is disabled or there is no current user, the only existing space switcher lived inside the account menu, so there was no reachable UI for changing spaces. The version marker also occupied header space that should remain available for navigation actions.

Playwright also caught that switching spaces while already on / refreshed the tree but not the visible root page, because the viewer only reloaded on path changes. The viewer now also watches active space changes.

Impact

Unauthenticated/public shell users can switch between spaces again. Authenticated users keep the same account-menu switching flow as before. The current page content follows the selected space even when the URL stays the same. The header stays more compact on mobile, while the version marker remains visible in the sidebar footer.