Add YubiKey and hardware security key guide

[DicksonWu654]

Closes #405

Summary

• add a practical account-management guide for YubiKeys and other hardware security keys
• link it from the account-management overview and generated section index
• add it to the Guides sidebar

Verification

• pnpm exec markdownlint-cli2 docs/pages/guides/account-management/hardware-security-keys.mdx docs/pages/guides/account-management/overview.mdx docs/pages/guides/account-management/index.mdx
• pnpm exec vocs build

[github-actions]

Sidebar Configuration Reminder

This PR includes added, renamed, or removed documentation files:

• docs/pages/guides/account-management/hardware-security-keys.mdx (added)

Please ensure that:

• The sidebar in vocs.config.tsx has been updated to include these files
• New content has the dev: true parameter so it's marked as under development
• Sidebar links match the file paths - use the preview deployment to verify

See Contributing Guide – Sidebar & Navigation for more details.

---

_{This is an automated reminder. If this PR doesn't need sidebar changes, you can ignore this message.}

[github-actions]

built with Refined Cloudflare Pages Action

⚡ Cloudflare Pages Deployment

Name	Status	Preview	Last Commit
frameworks	✅ Ready (View Log)	Visit Preview	cfcfb48

[github-actions]

Sidebar Configuration Reminder

Documentation files update:

New in this push:

• docs/pages/guides/endpoint-security/hardware-security-keys.mdx (added) ← NEW

Please ensure that:

• The sidebar in vocs.config.tsx has been updated to include these files
• New content has the dev: true parameter so it's marked as under development
• Sidebar links match the file paths - use the preview deployment to verify

See Contributing Guide – Sidebar & Navigation for more details.

---

_{This is an automated reminder. If this PR doesn't need sidebar changes, you can ignore this message.}

[scode2277]

GTG @mattaereal! Ty @DicksonWu654!