Remove the docker module: dotfiles no longer installs Docker

Installing Docker Engine is a host/image decision, not a per-user
environment one. In Coder workspaces (unprivileged pods, no systemd) the
module ran get.docker.com on every start for a daemon that can never
run there. Where Docker is wanted, install it on the host or bake it
into the image.

Also drops the zshrc newgrp-docker hook that existed only for this
module's group change, and the docs/skills references to docker/.
docker-rootless-cgroup/ (configures Kasm's existing rootless daemon)
and bin/'s kind gate (detects a daemon) stay.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

bootstrap.sh

@@ -66,7 +66,7 @@ fi
 #
 # WHY: these used to be bare calls, so under `set -eu` the FIRST failing module
 # aborted bootstrap and every later module silently never ran — one unsupported
-# distro in docker/ was enough to leave a box with no CLIs, no npx and no
+# distro in one module was enough to leave a box with no CLIs, no npx and no
 # ansible. The modules are independent, so a failure in one is not a reason to
 # skip the rest. (bin/install.sh does the same for individual tools; this is
 # that guard one level up.)
@@ -79,8 +79,6 @@ run_module() {
 
 run_module zsh
 run_module git
-# Runs before bin/ so the kind install gate can see the rootful daemon.
-run_module docker
 run_module bin
 # Needs op and jq from bin/. Runs before everything that consumes a secret, and
 # its output is loaded into THIS process so later modules see the vault's