The version selector does not consistently display all available documentation versions

### Environment (Required on creation)
https://docs.fluxnova.finos.org/manual/3.0/

### Description (Required on creation; please attach any relevant screenshots, stacktraces, log files, etc. to the ticket)

The version selector does not consistently display all available documentation versions.

After navigating to version 2.0, version 3.0 is no longer available in the version dropdown, preventing users from switching back to it through the UI.

### Steps to reproduce (Required on creation)

1. Open https://docs.fluxnova.finos.org/manual/3.0/
2. Open the version selector.
3. Select version 2.0.
4. Once redirected to the 2.0 documentation, open the version selector again.

### Observed Behavior (Required on creation)

Version 3.0 is no longer present in the version dropdown after switching to version 2.0.

### Expected behavior (Required on creation)

All available versions should remain visible in the version selector regardless of the currently selected version. After switching to 2.0, version 3.0 should still be available so users can navigate back to it.

### Breakdown
- PR in theme repo #35
- PR in manual repo https://github.com/finos/fluxnova-docs-manual/pull/54

### Dev2QA handover
- [ ] Does this ticket need a QA test and the testing goals are not clear from the description?