Merge gitea/act into act/

Merges the `gitea.com/gitea/act` fork into this repository as the `act/`
directory and consumes it as a local package. The `replace github.com/nektos/act
=> gitea.com/gitea/act` directive is removed; act's dependencies are merged
into the root `go.mod`.

- Imports rewritten: `github.com/nektos/act/pkg/...` → `gitea.com/gitea/act_runner/act/...`
  (flattened — `pkg/` boundary dropped to match the layout forgejo-runner adopted).
- Dropped act's CLI (`cmd/`, `main.go`) and all upstream project files; kept
  the library tree + `LICENSE`.
- Added `// Copyright <year> The Gitea Authors ...` / `// Copyright <year> nektos`
  headers to 104 `.go` files.
- Pre-existing act lint violations annotated inline with
  `//nolint:<linter> // pre-existing issue from nektos/act`.
  `.golangci.yml` is unchanged vs `main`.
- Makefile test target: `-race -short` (matches forgejo-runner).
- Pre-existing integration test failures fixed: race in parallel executor
  (atomic counters); TestSetupEnv / command_test / expression_test /
  run_context_test updated to match gitea fork runtime; TestJobExecutor and
  TestActionCache gated on `testing.Short()`.

Full `gitea/act` commit history is reachable via the second parent.

Co-Authored-By: Claude (Opus 4.7) <noreply@anthropic.com>

act/model/step_result.go

@@ -0,0 +1,49 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Copyright 2021 The nektos/act Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package model
+
+import "fmt"
+
+type stepStatus int
+
+const (
+	StepStatusSuccess stepStatus = iota
+	StepStatusFailure
+	StepStatusSkipped
+)
+
+var stepStatusStrings = [...]string{
+	"success",
+	"failure",
+	"skipped",
+}
+
+func (s stepStatus) MarshalText() ([]byte, error) {
+	return []byte(s.String()), nil
+}
+
+func (s *stepStatus) UnmarshalText(b []byte) error {
+	str := string(b)
+	for i, name := range stepStatusStrings {
+		if name == str {
+			*s = stepStatus(i)
+			return nil
+		}
+	}
+	return fmt.Errorf("invalid step status %q", str)
+}
+
+func (s stepStatus) String() string {
+	if int(s) >= len(stepStatusStrings) {
+		return ""
+	}
+	return stepStatusStrings[s]
+}
+
+type StepResult struct {
+	Outputs    map[string]string `json:"outputs"`
+	Conclusion stepStatus        `json:"conclusion"`
+	Outcome    stepStatus        `json:"outcome"`
+}