[FEATURE]: Support storing and autofilling Passkeys (WebAuthn / FIDO2)

[LubosKolouch]

⚠️ This issue respects the following points: ⚠️

• This is a feature request for one feature, not a question, discussion or multiple features.
• This is not a feature request for the browser extension or another client.
• This feature is not already requested on Github (I've searched it).
• This feature does not already exist (I checked the wiki).

Current Status

The extension suppors only passwords, not passkeys.

Feature Description

Description:
With more and more websites adopting passwordless authentication, it would be incredibly useful if the Nextcloud Passwords app and its browser extension could store and manage passkeys.

Use Case:
As a user migrating away from Google Password Manager / Apple Keychain to Nextcloud Passwords, I want to be able to save and sync passkeys so I can use the extension to log into modern passwordless services (like Google, GitHub, and Microsoft) seamlessly.

Proposed Solution:
Implement WebAuthn credential storage capabilities in the database and support the credential creation/assertion APIs in the browser extension, similar to how other modern password managers(e.g., Bitwarden, 1Password) now act as passkey providers.

Additional Context

No response