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/workflow_call_inputs/event.json

@@ -0,0 +1,6 @@
+{
+  "inputs": {
+    "required": "required input",
+    "boolean": "true"
+  }
+}

act/runner/testdata/workflow_call_inputs/workflow_call_inputs.yml

@@ -0,0 +1,36 @@
+name: workflow_call
+
+on:
+  workflow_call:
+    inputs:
+      required:
+        description: a required input
+        required: true
+      with_default:
+        description: an input with default
+        required: false
+        default: default
+      boolean:
+        description: an input of type boolean
+        required: false
+        type: boolean
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: test required input
+        run: |
+          echo input.required=${{ inputs.required }}
+          [[ "${{ inputs.required }}" = "required input" ]] || exit 1
+      - name: test input with default
+        run: |
+          echo input.with_default=${{ inputs.with_default }}
+          [[ "${{ inputs.with_default }}" = "default" ]] || exit 1
+      - id: boolean-test
+        name: run on boolean input
+        if: ${{ inputs.boolean == true }}
+        run: echo "::set-output name=value::executed"
+      - name: has boolean test?
+        run: |
+          [[ "${{ steps.boolean-test.outputs.value }}" = "executed" ]] || exit 1