Add a prebuilt tutabridge-bin package (downloads the published x86_64 CLI
binary, no Rust build) alongside the build-from-source tutabridge-git, each
in its own directory with a PKGBUILD and .SRCINFO. Update the maintainer
address and the packaging README for the two-package layout.
The sync Secret Service backend links system libdbus via libdbus-sys, so
the Linux CI job installs libdbus-1-dev + pkg-config and the PKGBUILD
declares dbus (build + runtime). Caught by the linux-cli CI job.
`tutabridge-git` VCS package builds only the headless CLI (no GUI/Node).
Handles the SDK submodule in prepare(), fetches crates for an offline
`--frozen` build, installs the binary + a systemd *user* unit (the
bridge runs per-user, binds localhost, uses the login keyring).
packaging/aur/README documents local build + AUR publish (.SRCINFO is
generated on Arch).
Anthony