Implement additional WebUI authentication methods (OAuth, OpenID, LDAP, SSO, etc.)

[nickna]

Currently, the WebUI only supports master key-based authentication for admin access. The documentation mentions support for additional authentication methods (local authentication, OAuth/OpenID Connect, LDAP/Active Directory, Single Sign-On), but these are not yet implemented.

Task: Add support for these authentication methods to the WebUI to enable more flexible and secure access control for different deployment environments.

• Local authentication (username/password)
• OAuth/OpenID Connect
• LDAP/Active Directory
• Single Sign-On (SSO)

Update the documentation and UI to reflect the newly supported authentication options.