Adds the tag-triggered workflow that builds 4 musl-linux + macOS
tarballs and attaches them to the tag's GitHub Release. Ships a
matching install guide (docs/install/binary.md) with SHA256SUMS
verify, systemd unit, upgrade flow, and hardware notes. Adds
[package.metadata.binstall] so 'cargo binstall oxicloud' works
automatically once the first release lands.
Also re-enables incremental compilation in the dev profile — the
'modest single-crate savings' rationale from when the crate was small
has been outgrown; full rebuild ~10 min is now the dev-loop bottleneck.
Edouard Vanbelle