Fix .deb build: install sqlite3 CLI package when using system libs

The runtime Dockerfile stage copies /usr/bin/sqlite3 from the builder.
When DEB_BUILD=true the custom SQLite build is skipped, so the sqlite3
CLI binary must come from the system sqlite3 package instead.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Prevent full systemd from being pulled in during cross-arch Docker bu…

…ilds

Debian sid recently changed a transitive dependency to pull in the full
systemd package instead of systemd-standalone-sysusers.  The full systemd
postinst crashes under QEMU ARM emulation (SIGSEGV in systemd 260.x),
breaking all arm/v7 and arm64 cross-architecture builds.

Pre-install systemd-standalone-sysusers before the main apt-get install
so the sysusers virtual dependency is already satisfied and apt doesn't
pull in the full systemd package.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>