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/runner/action_cache_offline_mode.go

@@ -0,0 +1,45 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// Copyright 2024 The nektos/act Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package runner
+
+import (
+	"context"
+	"io"
+	"path"
+
+	git "github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/plumbing"
+)
+
+type GoGitActionCacheOfflineMode struct {
+	Parent GoGitActionCache
+}
+
+func (c GoGitActionCacheOfflineMode) Fetch(ctx context.Context, cacheDir, url, ref, token string) (string, error) {
+	sha, fetchErr := c.Parent.Fetch(ctx, cacheDir, url, ref, token)
+	gitPath := path.Join(c.Parent.Path, safeFilename(cacheDir)+".git")
+	gogitrepo, err := git.PlainOpen(gitPath)
+	if err != nil {
+		return "", fetchErr
+	}
+	refName := plumbing.ReferenceName("refs/action-cache-offline/" + ref)
+	r, err := gogitrepo.Reference(refName, true)
+	if fetchErr == nil {
+		if err != nil || sha != r.Hash().String() {
+			if err == nil {
+				refName = r.Name()
+			}
+			ref := plumbing.NewHashReference(refName, plumbing.NewHash(sha))
+			_ = gogitrepo.Storer.SetReference(ref)
+		}
+	} else if err == nil {
+		return r.Hash().String(), nil
+	}
+	return sha, fetchErr
+}
+
+func (c GoGitActionCacheOfflineMode) GetTarArchive(ctx context.Context, cacheDir, sha, includePrefix string) (io.ReadCloser, error) {
+	return c.Parent.GetTarArchive(ctx, cacheDir, sha, includePrefix)
+}