Support efficient multi-architecture builds (amd64 & arm64) in build system

[sheurich]

As a developer and maintainer, I want the build system to efficiently support both amd64 and arm64 architectures so that:

• Local development builds only target the current architecture for faster builds
• An explicit architecture flag can override and build for another supported architecture
• GitHub Actions can be configured to use parallel runners for different architectures in the future
• The existing release workflow continues to work without modification

Current Problem

The current build scripts and container files assume or force amd64 output, making it impossible to build arm64 artifacts. Additionally, platform-specific arguments are missing in supporting scripts, causing failures in containerized builds for ARM.

Acceptance Criteria

• Local builds detect and build only the current host architecture unless explicitly overridden
• Build system supports running on both ARM and x86 systems
• Test command GO_VERSION=1.24.6 ./tools/container-build.sh works on both ARM and x86 systems
• Generated artifacts include proper architecture labels (e.g., .arm64.tar.gz, .amd64.deb)
• No breaking changes to existing workflows
• Foundation laid for future parallel multi-architecture CI builds

[aarongable]

Resolved by #8547