refactor: move act under internal

The runner is an application, not a library. `act/model` and
`act/exprparser` were the last packages anything outside this repository
consumed and they now live in actionslib, so nothing needs the rest of
`act` to be importable, and keeping it importable invites the coupling
that was just removed.

Import paths only, the files are unchanged.

Assisted-by: Codet:GPT-5.1-Codex

internal/act/runner/helpers_test.go

@@ -0,0 +1,52 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package runner
+
+import (
+	"context"
+	"os/exec"
+	"runtime"
+	"testing"
+
+	"gitea.com/gitea/runner/internal/act/container"
+
+	mobyclient "github.com/moby/moby/client"
+)
+
+// requireLinuxDocker skips on non-Linux hosts. Some integration workflows need Docker features
+// that only a Linux daemon provides (host networking, host /proc bind mounts); Docker Desktop
+// on macOS/Windows does not, so those tests can only run on Linux.
+func requireLinuxDocker(t *testing.T) {
+	t.Helper()
+	if runtime.GOOS != "linux" {
+		t.Skip("skipping: requires a Linux Docker host")
+	}
+}
+
+// requireDocker skips the test unless a reachable docker daemon is available.
+// GetDockerClient succeeds even without a running daemon (its ping is best-effort),
+// so the daemon has to be pinged explicitly here to decide whether to skip.
+func requireDocker(t *testing.T) {
+	t.Helper()
+	ctx := context.Background()
+	cli, err := container.GetDockerClient(ctx)
+	if err != nil {
+		t.Skipf("skipping: docker client unavailable: %v", err)
+	}
+	defer cli.Close()
+	if _, err := cli.Ping(ctx, mobyclient.PingOptions{}); err != nil {
+		t.Skipf("skipping: docker daemon unreachable: %v", err)
+	}
+}
+
+// requireHostTools skips the test unless every named executable is on PATH. Used by the
+// self-hosted (host environment) suite, which runs steps directly on the host.
+func requireHostTools(t *testing.T, tools ...string) {
+	t.Helper()
+	for _, tool := range tools {
+		if _, err := exec.LookPath(tool); err != nil {
+			t.Skipf("skipping: required host tool %q not found: %v", tool, err)
+		}
+	}
+}