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/node20/node_modules/is-plain-object/LICENSE

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2014-2017, Jon Schlinkert.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

act/runner/testdata/actions/node20/node_modules/is-plain-object/is-plain-object.d.ts

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+export function isPlainObject(o: any): boolean;

act/runner/testdata/actions/node20/node_modules/is-plain-object/package.json

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+{
+  "name": "is-plain-object",
+  "description": "Returns true if an object was created by the `Object` constructor, or Object.create(null).",
+  "version": "5.0.0",
+  "homepage": "https://github.com/jonschlinkert/is-plain-object",
+  "author": "Jon Schlinkert (https://github.com/jonschlinkert)",
+  "contributors": [
+    "Jon Schlinkert (http://twitter.com/jonschlinkert)",
+    "Osman Nuri Okumuş (http://onokumus.com)",
+    "Steven Vachon (https://svachon.com)",
+    "(https://github.com/wtgtybhertgeghgtwtg)",
+    "Bogdan Chadkin (https://github.com/TrySound)"
+  ],
+  "repository": "jonschlinkert/is-plain-object",
+  "bugs": {
+    "url": "https://github.com/jonschlinkert/is-plain-object/issues"
+  },
+  "license": "MIT",
+  "main": "dist/is-plain-object.js",
+  "module": "dist/is-plain-object.mjs",
+  "types": "is-plain-object.d.ts",
+  "files": [
+    "is-plain-object.d.ts",
+    "dist"
+  ],
+  "exports": {
+    ".": {
+      "import": "./dist/is-plain-object.mjs",
+      "require": "./dist/is-plain-object.js"
+    },
+    "./package.json": "./package.json"
+  },
+  "engines": {
+    "node": ">=0.10.0"
+  },
+  "scripts": {
+    "build": "rollup -c",
+    "test_browser": "mocha-headless-chrome --args=disable-web-security -f test/browser.html",
+    "test_node": "mocha -r esm",
+    "test": "npm run test_node && npm run build && npm run test_browser",
+    "prepare": "rollup -c"
+  },
+  "devDependencies": {
+    "chai": "^4.2.0",
+    "esm": "^3.2.22",
+    "gulp-format-md": "^1.0.0",
+    "mocha": "^6.1.4",
+    "mocha-headless-chrome": "^3.1.0",
+    "rollup": "^2.22.1"
+  },
+  "keywords": [
+    "check",
+    "is",
+    "is-object",
+    "isobject",
+    "javascript",
+    "kind",
+    "kind-of",
+    "object",
+    "plain",
+    "type",
+    "typeof",
+    "value"
+  ],
+  "verb": {
+    "toc": false,
+    "layout": "default",
+    "tasks": [
+      "readme"
+    ],
+    "plugins": [
+      "gulp-format-md"
+    ],
+    "related": {
+      "list": [
+        "is-number",
+        "isobject",
+        "kind-of"
+      ]
+    },
+    "lint": {
+      "reflinks": true
+    }
+  }
+}