ProximityConfig
In-person presentment (QR engagement + BLE).
Parameters
offerCentralClientMode
wallet role: also offer BLE central client mode (the wallet runs the BLE link) in the engagement QR, listed first. Verifiers that support it pick it automatically; others use peripheral server mode as before. Only takes effect on Android, whose central can request the fastest link (iOS can't, so an iOS wallet always leaves the link to the verifier). Default on; turn off to offer peripheral server mode only.