docs: explain linux-libc-dev dependency

[eugene-harold-krabs]

Summary

• document why prepare-tool all retains linux-libc-dev
• identify the Conan C++ toolchain dependency chain
• clarify that purging the package would break the prepared compiler package dependencies

Investigation

prepare-tool all includes ConanPrepareService, which installs gcc and g++. On Ubuntu, g++ pulls the C++ development packages, libstdc++-13-dev depends on libc6-dev, and libc6-dev depends on linux-libc-dev. The package is therefore required by the image contract rather than an orphaned build dependency.

Validation

• pnpm prettier
• git diff --check

Closes #1525

[eugene-harold-krabs]

Thank you for maintaining containerbase/sidecar and for your time. After revisiting the original report, this is not a Renovate or sidecar defect: linux-libc-dev is a required transitive dependency of the prepared C/C++ toolchain. I am withdrawing this documentation change and closing the related issue. Sorry for the noise, and thanks again.