Build ARM64 musl release in Alpine

[frankmanzhu]

What changed

• Adds scripts/package-release-alpine.sh to package aarch64-unknown-linux-musl inside an ARM64 Alpine Rust container.
• Uses Alpine build-base, cmake, binutils, file, pkgconf, and python3 for a real musl C/C++ build environment.
• Keeps the existing Zig packaging path for the other Unix release targets.
• Adds a ZM_USE_SYSTEM_MUSL_TOOLCHAIN=1 path in scripts/package-release.sh so the Alpine build uses system cc/c++/ar instead of Zig.
• Keeps the Linux install guide aligned with the static runtime guarantee asserted by CLI integration tests.

Why

The Linux ARM64 musl package build failed when sha2-asm compiled its AArch64 .S source through the Zig wrapper. This tries a native ARM64 Alpine musl environment instead, preserving the SHA2 assembly path and avoiding a software fallback unless this approach still fails.

Validation

• bash -n scripts/package-release.sh scripts/package-release-alpine.sh
• cargo test -p zmanager-cli --test help_cli linux_release_artifacts_are_static_tarballs
• cargo tree --locked --target aarch64-unknown-linux-musl -i sha2-asm confirms sha2-asm remains in the ARM64 musl dependency tree.
• Repository branding guardrail scan completed with no matches.

Full release packaging is intentionally left for GitHub Actions on the ARM64 runner.