feat(release): aarch64-unknown-linux-musl build

[kleyt0n]

Problem

install.sh:49-52 hard-fails arm64 users on older glibc with no static build for $arch — build from source, while x86-64 falls back to musl.

What to do

• Add the target to .github/workflows/release.yml.
• Needs a cross C toolchain for bundled SQLite — the cross job in .github/workflows/ci.yml already demonstrates the pattern with CC_<target> for the two existing cross targets.
• Replace the hard failure in install.sh with the musl fallback arm64 currently lacks.

Acceptance

An arm64 Linux machine below the glibc 2.35 floor installs successfully.