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/common/job_error.go

@@ -0,0 +1,34 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Copyright 2021 The nektos/act Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package common
+
+import (
+	"context"
+)
+
+type jobErrorContextKey string
+
+const jobErrorContextKeyVal = jobErrorContextKey("job.error")
+
+// JobError returns the job error for current context if any
+func JobError(ctx context.Context) error {
+	val := ctx.Value(jobErrorContextKeyVal)
+	if val != nil {
+		if container, ok := val.(map[string]error); ok {
+			return container["error"]
+		}
+	}
+	return nil
+}
+
+func SetJobError(ctx context.Context, err error) {
+	ctx.Value(jobErrorContextKeyVal).(map[string]error)["error"] = err
+}
+
+// WithJobErrorContainer adds a value to the context as a container for an error
+func WithJobErrorContainer(ctx context.Context) context.Context {
+	container := map[string]error{}
+	return context.WithValue(ctx, jobErrorContextKeyVal, container)
+}