feat(auth-emulator): Add mock Passkey (WebAuthn) support

[macastelaz]

Description

Add support to the auth emulator for the passkey API surface. Passkey support is currently in "private preview" on a feature branch of the firebase web auth SDK (https://github.com/firebase/firebase-js-sdk/tree/passkey) and we are working towards a beta release which will involve updating the auth quickstart that in turn relies on the auth emulator.

Scenarios Tested

Using a locally modified quickstart version with passkey support pointing at a locally running auth emulator with these changes (https://screenshot.googleplex.com/3EbEZapL5Ax8o8h.png) I manually verified:

• Sign in with passkey
• Enrolling a passkey
• Unerolling a passkey
• Getting passkeys enrolled for a user

[gemini-code-assist]

Code Review

This pull request introduces passkey support to the Auth emulator. It adds passkey enrollment and sign-in operations, updates the OpenAPI spec generation scripts, and implements the corresponding backend emulator logic in operations.ts and state.ts. Feedback on the changes suggests improving type safety by avoiding any casts when parsing authenticator responses and avoiding the non-null assertion operator (!) when filtering passkeys to delete.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.47826% with 3 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@cabdf4c). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/emulator/auth/operations.ts	93.33%	0 Missing and 3 partials ⚠️

Additional details and impacted files

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  Coverage        ?   57.41%           
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  Hits            ?    22062           
  Misses          ?    14576           
  Partials        ?     1789           

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