docs(readme): add OpenSSF Best Practices badge

[michalharakal]

Adds the OpenSSF Best Practices badge for project 14004 to the README badge row, next to the existing OpenSSF Scorecard badge.

[![OpenSSF Best Practices](https://www.bestpractices.dev/projects/14004/badge)](https://www.bestpractices.dev/projects/14004)

Heads-up: it currently renders "in progress 24%", not "passing"

The badge image is generated live from the project's current criteria state, and right now that is:

{ "id": 14004, "name": "SKaiNET", "badge_level": "in_progress", "tiered_percentage": 24 }

so the SVG renders openssf best practices: in progress 24%. The /en/projects/14004/passing URL is the passing-level criteria page — the tab listing what passing requires — not a statement that the project has reached it.

Nothing to fix in this PR: the badge is dynamic and flips to passing on its own once the criteria are filled in at https://www.bestpractices.dev/en/projects/14004/passing. Merging now means the README tracks that progress rather than needing a follow-up edit. If you'd rather the row only ever show green badges, hold this until the percentage is up.

Also worth noting the badge is linked to the un-suffixed project URL (/projects/14004) rather than /en/projects/14004/passing, so it lands on the project overview in the reader's own language and does not go stale if the project later moves to silver or gold.

Verification

• https://www.bestpractices.dev/projects/14004/badge → HTTP 200, valid SVG
• repo_url on the project record is https://github.com/SKaiNET-developers/SKaiNET, so the badge points at this repo
• README-only change; no build or CI impact