feat(core): passkey management core changes

[NaveenChand755]

Summary

Adds core passkey infrastructure (types, WebAuthn utils, i18n) to the my-account package. Also cleans up redundant MFA exports from index.ts and user-passkey-service hook

Why

• React passkey components need these building blocks before they can be built
• Follows the same pattern MFA uses for consistency
• Duplicate exports were dead weight
• adds user passkey service hook required for the user passkey hook

What

• Passkey service layer — SDK types, React Query keys, WebAuthn browser utils
• Passkey i18n — English strings + PasskeyMessages interface for consumer overrides
• Removed duplicate MFA named exports already covered by export *

Packages

• packages/core
• packages/react
• examples

References

Testing

How can this be verified? Note anything intentionally not covered by tests and why.

• This change adds unit test coverage
• Tested for both SPA and RWA flows, all example apps working
• All existing and new tests complete without errors

Checklist

• Breaking change
• Requires docs update
• Backward compatible

Contributing

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.55%. Comparing base (aecf241) to head (07eb204).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #304      +/-   ##
==========================================
+ Coverage   89.47%   89.55%   +0.08%     
==========================================
  Files         156      159       +3     
  Lines       13070    13178     +108     
  Branches     1419     1827     +408     
==========================================
+ Hits        11694    11802     +108     
  Misses       1376     1376              

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