Improve code quality across metadata, nav state, and content links

[jotalis]

Summary

• improve root metadata descriptions for better SEO/OpenGraph defaults
• fix stale legal links in Terms of Service to use the current icssc.club privacy policy URL
• make mobile navigation dialog state updates deterministic by using onOpenChange={setOpen}
• harden nav notification storage logic against unavailable localStorage
• avoid invalid empty project links by using conditional rendering for project image wrappers
• normalize project data by removing empty-string projectLink
• stabilize candidate statement paragraph keys to avoid potential key collisions
• keep project images exposed to assistive tech when no project link exists

Validation

• pnpm install --prod
• pnpm build (fails due to existing module resolution issues in this environment unrelated to these edits)
• pnpm lint (blocked because devDependencies are not installed; full install currently fails from upstream lockfile tarball https://pkg.pr.new/@opennextjs/aws@748 returning 404)