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/testdata/actions/node16/node_modules/universal-user-agent/dist-node/index.js

@@ -0,0 +1,18 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', { value: true });
+
+function getUserAgent() {
+  if (typeof navigator === "object" && "userAgent" in navigator) {
+    return navigator.userAgent;
+  }
+
+  if (typeof process === "object" && "version" in process) {
+    return `Node.js/${process.version.substr(1)} (${process.platform}; ${process.arch})`;
+  }
+
+  return "<environment undetectable>";
+}
+
+exports.getUserAgent = getUserAgent;
+//# sourceMappingURL=index.js.map

act/runner/testdata/actions/node16/node_modules/universal-user-agent/dist-node/index.js.map

@@ -0,0 +1 @@
+{"version":3,"file":"index.js","sources":["../dist-src/index.js"],"sourcesContent":["export function getUserAgent() {\n    if (typeof navigator === \"object\" && \"userAgent\" in navigator) {\n        return navigator.userAgent;\n    }\n    if (typeof process === \"object\" && \"version\" in process) {\n        return `Node.js/${process.version.substr(1)} (${process.platform}; ${process.arch})`;\n    }\n    return \"<environment undetectable>\";\n}\n"],"names":["getUserAgent","navigator","userAgent","process","version","substr","platform","arch"],"mappings":";;;;AAAO,SAASA,YAAT,GAAwB;AAC3B,MAAI,OAAOC,SAAP,KAAqB,QAArB,IAAiC,eAAeA,SAApD,EAA+D;AAC3D,WAAOA,SAAS,CAACC,SAAjB;AACH;;AACD,MAAI,OAAOC,OAAP,KAAmB,QAAnB,IAA+B,aAAaA,OAAhD,EAAyD;AACrD,WAAQ,WAAUA,OAAO,CAACC,OAAR,CAAgBC,MAAhB,CAAuB,CAAvB,CAA0B,KAAIF,OAAO,CAACG,QAAS,KAAIH,OAAO,CAACI,IAAK,GAAlF;AACH;;AACD,SAAO,4BAAP;AACH;;;;"}