Support multiple bonded hosts without requiring factory reset

[Swissola]

Summary

• Tracks the current connection peer BD address via the extended onConnect(BLEServer*, esp_ble_gatts_cb_param_t*) overload
• Adds bleRemoveCurrentBond() which removes only the currently connected peer LTK from NVS
• The unpair JSON command now calls bleRemoveCurrentBond() instead of bleClearBonds(), so each host unpairs itself independently
• bleClearBonds() is preserved unchanged and still called on factory reset

Motivation

The existing unpair command wipes all stored bonds, which means switching between a home PC and work laptop requires a full factory reset and re-pairing both devices. The ESP32 BLE stack supports up to 7 simultaneous bonds — this change makes full use of that by letting each host manage its own bond independently.

Behaviour after this change

• Multiple hosts (e.g. desktop + laptop + Pi) can all bond and auto-reconnect without interfering with each other
• A host sending {"cmd":"unpair"} removes only its own bond
• First-time pairing with a new host works identically to before (passkey flow unchanged)
• Factory reset still wipes all bonds via bleClearBonds()
• No changes to the wire protocol or JSON command structure
• LE Secure Connections + MITM security model preserved

Test plan

• Pair two hosts, unpair one, confirm the other still auto-reconnects
• Factory reset clears all bonds
• New host pairing passkey flow works as before
• bleConnected() / bleSecure() / blePasskey() behaviour unchanged

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