Configurable identity matching for sign-in

Configurable identity matching for sign-in: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). We're laying the groundwork for passwordless / unified sign-in, where a user types a single "identity" value (an email, a phone number, a username, ...) into one field and we have to…