Implement SRAM AXS encrypted drivetrain support

[cagnulein]

Summary

• add SRAM AXS BLE discovery and encrypted SRAMBond v1 pairing
• persist per-device keys and decrypt authenticated AES-128 EAX drivetrain packets
• decode rear-derailleur position and map gear changes to QZ virtual gearing
• add SRAM AXS settings and deterministic protocol tests

Context

Fixes #2768: #2768

The SRAM AXS protocol implementation was taken from and cross-checked against GaborWnuk/sram-axs, including the documented SRAMBond v1 exchange, AES-EAX behavior, fixtures, and drivetrain status decoding. The implementation is adapted to QZ's Qt/C++ architecture.

Validation

• git diff --cached --check
• python3 -m json.tool src/settings-catalog.json
• clang syntax checks for the new Qt/C++ translation units
• deterministic DH, AES-EAX, and protobuf protocol tests added
• full qmake/gtest runtime was not run because the installed Qt qmake binaries are x86-only on this ARM host