M1 Beta: Prepare NFC and fingerprint identity support

[mastertape]

Roadmap reference: docs/roadmap/m1-dhl-retrofit-beta.md

Prepare the beta identity model and hardware assumptions for NFC and optional fingerprint support.

Acceptance criteria:

• NFC reader candidate interface is documented.
• NFC token enrollment flow is sketched.
• NFC token IDs are mapped to person/household identities.
• Fingerprint support is represented as optional/prepared in the data model.
• Fingerprint module interface options are listed.
• Security/privacy notes for biometric use are documented.
• Wiegand, UART or other relevant interfaces are compared for the actual modules.
• Beta can ship with fingerprint disabled if the architecture is prepared.