v1.1.0

Add OS flavour overlays for environment classes that share a GOOS (and
often a distro ID) but need different files. The first built-in flavour
is wsl: place entries under .os/linux/.flavour/wsl/, detect WSL at
runtime, and store with rigo add --flavour wsl. Layer order (later
wins) is common → OS → distro → flavour. Document when to use
[include] / [exclude] versus flavours. Also stream file comparisons
for status/apply, probe Windows symlink capability once before linking,
and expand unit tests around volumes and CLI helpers.