Build hiy-server targeting aarch64-unknown-linux-musl so the binary
has no glibc dependency at all, making the runtime image irrelevant
to glibc version mismatches. Uses rustls (already in Cargo.toml) so
no OpenSSL vendoring needed. SQLite is bundled by sqlx.
rust:1.77-slim has drifted to a newer Debian base with glibc 2.39,
but debian:bookworm-slim only has glibc 2.36, causing a GLIBC_2.39
not found error at runtime. Pinning to the explicit bookworm variant
keeps both stages on the same glibc version.
