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/step_factory_test.go

@@ -0,0 +1,85 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// Copyright 2022 The nektos/act Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package runner
+
+import (
+	"testing"
+
+	"gitea.dev/actionslib/pkg/model"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestStepFactoryNewStep(t *testing.T) {
+	table := []struct {
+		name  string
+		model *model.Step
+		check func(s step) bool
+	}{
+		{
+			name: "StepRemoteAction",
+			model: &model.Step{
+				Uses: "remote/action@v1",
+			},
+			check: func(s step) bool {
+				_, ok := s.(*stepActionRemote)
+				return ok
+			},
+		},
+		{
+			name: "StepLocalAction",
+			model: &model.Step{
+				Uses: "./action@v1",
+			},
+			check: func(s step) bool {
+				_, ok := s.(*stepActionLocal)
+				return ok
+			},
+		},
+		{
+			name: "StepDocker",
+			model: &model.Step{
+				Uses: "docker://image:tag",
+			},
+			check: func(s step) bool {
+				_, ok := s.(*stepDocker)
+				return ok
+			},
+		},
+		{
+			name: "StepRun",
+			model: &model.Step{
+				Run: "cmd",
+			},
+			check: func(s step) bool {
+				_, ok := s.(*stepRun)
+				return ok
+			},
+		},
+	}
+
+	for _, tt := range table {
+		t.Run(tt.name, func(t *testing.T) {
+			sf := &stepFactoryImpl{}
+
+			step, err := sf.newStep(tt.model, &RunContext{})
+
+			assert.True(t, tt.check((step)))
+			assert.NoError(t, err)
+		})
+	}
+}
+
+func TestStepFactoryInvalidStep(t *testing.T) {
+	model := &model.Step{
+		Uses: "remote/action@v1",
+		Run:  "cmd",
+	}
+
+	sf := &stepFactoryImpl{}
+
+	_, err := sf.newStep(model, &RunContext{})
+
+	assert.Error(t, err)
+}