Remove retired Mastodon and Threads accounts

[manishtiwari25]

Summary

• remove the retired Lamplit Labs Mastodon and Threads accounts from shared social data, homepage surfaces, and Organization JSON-LD
• remove their unused custom icons and icon mappings
• remove the retired account links from the README

Validation

• npm run lint
• npm run typecheck
• npm run build
• rendered homepage assertions verify the retired links/labels are absent and remaining sameAs ordering is preserved
• residual tracked-file searches found no Lamplit Labs/Bites In Byte Mastodon or Threads account URLs

No test script exists in this repository.