Update home pages of 3.8 and 3.9 docs in Japanese; update Japanese category names in sidebar navigation

[josh-wong]

Description

This PR updates the home pages of the ScalarDL 3.8 and 3.9 docs to help guide users to certain docs in each section.

This PR also fixes some related translations and adds "Unsupported" wording to the 3.7 docs in the dropdown menu when on Japanese docs.

Related issues and/or PRs

N/A

Changes made

• Added Card components for ScalarDL 3.8 and 3.9.
• Revised index.mdx for 3.8 and 3.9 to use the Card components.
• Marked 3.7 as out of support in the dropdown menu for the Japanese documentation.
• Updated side navigation according to comments in a PR about sidebar navigation wording for the ScalarDB docs site.

Checklist

The following is a best-effort checklist. If any items in this checklist are not applicable to this PR or are dependent on other, unmerged PRs, please still mark the checkboxes after you have read and understood each item.

• I have updated the side navigation as necessary.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• Any remaining open issues linked to this PR are documented and up-to-date (Jira, GitHub, etc.).
• My changes generate no new warnings.
• Any dependent changes in other PRs have been merged and published.

Additional notes (optional)

N/A