swarmexec v1.2.0 — manage Docker contexts from the client

New `swarmexec context` command group (alias `ctx`): create, ls, use, rm.
It writes docker's own on-disk context store, so contexts created here are
interchangeable with the docker CLI — and you no longer need docker
installed even to create one.

- context create <name> --docker-host <ssh://|tcp://|unix://|npipe://> [--description] [--use]
- context ls [--json]   context use <name>   context rm <name>… [-f]

Pure local file operations; no wire-protocol change, a running agent stays
compatible. The /docs page documents the new command.

Also: first release to run the deploy-site CI trigger (from "added trigger").