Add Credential Manager support and improve WebAuthnLinux authenticator functionality

[Karloss1234]

Core authenticator improvements (webauthn-authenticator.js)

Major improvements have been made to the WebAuthn authenticator implementation. It is now a functional Linux software Passkey authenticator with built-in credential management capabilities.

Summary

This PR improves WebAuthnLinux by adding Credential Manager functionality, improving credential persistence, and strengthening browser/native messaging integration.

The main areas changed are:

• Credential management and storage (view, rename, and delete credentials)
• Authenticator state handling
• WebAuthn metadata improvements
• Firefox and Chrome compatibility improvements
• Native messaging installation improvements
• Extensive testing on Kubuntu and Fedora with Firefox and Chrome

Testing has successfully verified Passkey registration and login with:

• Google
• Microsoft
• GitHub
• Government tax reporting websites
• webauthn.io

Specific changes

Credential management

• Added improved credential storage handling and persistence.
• Improved loading and saving of system_credentials through browser storage.
• Added reliable credential retrieval after extension restart.
• Improved handling of stored credential metadata.
• Added credential management operations including renaming and deleting credentials.

Authenticator reliability

• Improved authenticator initialisation and state handling.
• Improved asynchronous storage operations using modern Promise/async patterns.
• Reduced the risk of credential storage inconsistencies.
• Improved handling of authenticator state across browser sessions.

WebAuthn compatibility

• Improved authenticator metadata handling, including AAGUID management.
• Improved compatibility with browser WebAuthn flows.
• Maintained compatibility with existing WebAuthn registration and authentication processes.

Native messaging installation improvements

• Simplified native host installation.
• Removed the need for users to manually create the native messaging manifest.
• Added support for different Firefox configuration paths used by distributions such as Fedora.
• Improved installer verification output.

Debugging and development

• Added additional logging around credential operations and storage events.
• Improved visibility of authenticator state transitions during testing.

Breaking changes

None expected. Existing registered credentials remain usable.