[Smart Accounts Kit] Add passkey as a signer

[AyushBherwani1998]

Description

• Adds new guide for passkey as a signer

Issue(s) fixed

Fixes #2424

Preview

Checklist

• If this PR updates or adds documentation content that changes or adds technical meaning, it has received an approval from an engineer or DevRel from the relevant team.
• If this PR updates or adds documentation content, it has received an approval from a technical writer.

External contributor checklist

• I've read the contribution guidelines.
• I've created a new issue (or assigned myself to an existing issue) describing what this PR addresses.

---

Note

Adds a Passkey signer guide and links it in the sidebar and signer index, plus minor wording updates across existing signer guides.

• Docs:
  • New guide: smart-accounts-kit/guides/smart-accounts/signers/passkey.md detailing setup of a passkey (WebAuthn/P-256) signer and smart account configuration.
  • Navigation:
    • Add guides/smart-accounts/signers/passkey to gator-sidebar.js.
    • Add Passkey card to smart-accounts-kit/guides/smart-accounts/signers/index.md.
  • Copy updates:
    • Standardize info notes to "This guide supports React and React-based frameworks." in dynamic.md, embedded-wallets.md, and privy.md.

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Project	Deployment	Review	Updated (UTC)
metamask-docs	Ready	Preview, Comment	Dec 15, 2025 2:41pm

[m4sterbunny]

let some minor nits else, lgtm

[m4sterbunny]

lgtm