Add CLI and server version output

[0xShug0]

Summary

• add --version to audiocpp_cli and audiocpp_server
• report audio.cpp version, git commit/date, build type, compiler/platform, and compiled backends
• print a compact build summary plus a help hint for no-argument CLI launches
• keep source builds on the neutral dev version by default; release/dev packaging can inject -DAUDIOCPP_VERSION=...

Fixes #461

Validation

• built audiocpp_cli and audiocpp_server in Debug with CPU/CUDA/Vulkan enabled
• validated audiocpp_cli --version
• validated audiocpp_server --version
• validated audiocpp_cli --version --backend cpu stays clean
• validated no-argument CLI prints build summary and Run audiocpp_cli --help for usage.
• configured and built a separate Debug CPU/Vulkan-only build; version output reports backends: cpu,vulkan
• validated explicit -DAUDIOCPP_VERSION=0.7.2-dev override works for CLI and server

Follow up: Accept version in CI.