feat(web): redesign homepage with trust strip, GitHub nav link, and mirror footer (#3413)

[idling11]

• web/app/[locale]/page.tsx: add trust strip below hero showing MIT license, local-first, provider count, and security model
• web/components/nav.tsx: add GitHub link to main nav (EN + ZH)
• web/components/footer.tsx: add mirror/provenance links (CNB, Tsinghua)

Close #3413.

Testing

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features
• cargo test --workspace --all-features

Checklist

• Updated docs or comments as needed
• Added or updated tests where relevant
• Verified TUI behavior manually if UI changes
• Harvested/co-authored credit uses a GitHub numeric noreply address

[Hmbown]

Thanks @idling11. I am leaving this homepage redesign out of the 0.8.67 release cut because it now conflicts with current main and the public-site surface deserves a focused visual/content review instead of a last-minute merge. I would like to revisit it after the release, with your authorship preserved, either by rebase or by harvesting a compatible slice.