Add metadata schema selection to the landing page

Currently, SMECS supports curation workflows for both CodeMeta and ERSmeta schemas, but these functionalities are implemented and accessed separately.

We want to introduce a metadata schema selection step on the landing page, allowing users to choose which schema they want to use before starting the curation process.

The selected schema should determine how the curation page is structured. This should also provide an extensible foundation for adding more metadata schemas in the future.

Desired behavior:

1. On the landing page, the user can select a metadata schema.
2. Initially, the available options are:

• CodeMeta
• ERSmeta
• Later (ConnOSS schema)

3. The selected schema is carried into the curation workflow.
4. The curation page is structured according to the selected schema (tabs).

This issue can be done in parallel to https://github.com/NFDI4Energy/SMECS/issues/312.

Start at the landing page and trace how the curation workflow reaches the curation page and its tabs, then inspect the existing CodeMeta and ERSmeta implementations. Done means users can select CodeMeta or ERSmeta before curation, the choice is carried through the workflow, and the curation tabs follow that schema while leaving room for additional schemas.