docs(authentication): document SHORTCAKE_PASSKEY companion linking

[jlucaso1]

Summary

Documents the new passkey (SHORTCAKE_PASSKEY) companion-linking flow added in whatsapp-rust#928, the third authentication method alongside QR code and pair code linking.

• concepts/authentication.mdx — new "Passkey linking (SHORTCAKE_PASSKEY)" section: how the flow works (mermaid sequence diagram), the PasskeyAuthenticator trait/seam, automatic vs. manual driving modes, re-link handoff (skip_handoff_ux), events, and client methods. Overview updated from two to three methods.
• concepts/events.mdx — adds PairPasskeyRequest, PairPasskeyConfirmation, and PairPasskeyError to the Event enum listing and the Pairing Events section.
• api/client.mdx — documents set_passkey_authenticator, send_passkey_response, and send_passkey_confirmation, including PasskeyError variants.
• api/wacore.mdx — adds the shortcake module (pure crypto/protobuf core) to the Connection & Pairing module list.
• introduction.mdx — adds a passkey linking bullet to the Authentication feature list.

Content was written after reading the merged PR's diff, the new wacore/src/shortcake.rs/src/passkey/mod.rs/src/passkey/flow.rs source, and the updated wacore/src/types/events.rs to keep struct fields, method signatures, and error variants accurate.

Test plan

• Mintlify build/preview renders the new sections and mermaid diagram correctly
• Cross-reference anchors (/concepts/authentication#..., /api/client#...) resolve correctly

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Generated by Claude Code

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Summary by cubic

Adds docs for passkey linking (SHORTCAKE_PASSKEY) as the third authentication option, covering the flow, events, and client API. Clarifies that automatic mode only auto-confirms proven re-links; fresh links still require manual confirmation after showing the code.

• New Features
  • concepts/authentication.mdx: Passkey linking section with flow, PasskeyAuthenticator, auto/manual modes, re-link handoff, explicit note that fresh links need manual confirmation, events, and client calls.
  • concepts/events.mdx: Documents PairPasskeyRequest, PairPasskeyConfirmation, PairPasskeyError.
  • api/client.mdx: Adds set_passkey_authenticator, send_passkey_response, send_passkey_confirmation, and PasskeyError variants.
  • api/wacore.mdx: Adds the shortcake module description and link to auth docs.
  • introduction.mdx: Adds passkey linking to the feature list.

^{Written for commit 36df5a1. Summary will update on new commits.}

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📥 Commits

Reviewing files that changed from the base of the PR and between a5e47c0 and 36df5a1.

📒 Files selected for processing (5)

• api/client.mdx
• api/wacore.mdx
• concepts/authentication.mdx
• concepts/events.mdx
• introduction.mdx

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Project	Status	Preview	Updated (UTC)
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No issues found across 5 files

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