Add the shared packages for the sharks stack

model, tunnel, wg, authtoken, netguard, docker and dotenv, split out of the
original single repository so Hammerhead, Blacktip and Bamboo can live in
their own repos and import them. README extended; LICENSE unchanged.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docker/pipe_windows.go

@@ -0,0 +1,16 @@
+//go:build windows
+
+package docker
+
+import (
+	"context"
+	"net"
+
+	"github.com/Microsoft/go-winio"
+)
+
+func dialPipe(path string) func(ctx context.Context, network, addr string) (net.Conn, error) {
+	return func(ctx context.Context, _, _ string) (net.Conn, error) {
+		return winio.DialPipeContext(ctx, path)
+	}
+}