fix: align common behaviour with GitHub's runner (#1413)

Closes differences from GitHub's runner that common workflows hit:

- `ACTIONS_STEP_DEBUG` set as a repository variable enables debug output as on GitHub, where a secret of the same name still takes precedence. `runner.debug` and `RUNNER_DEBUG` are now also set inside composite actions, which lost the secret.
- `github.env` and `github.path` hold the file-command paths instead of being empty, so `echo "A=1" >> "${{ github.env }}"` works.
- Remote composite actions only get a pre stage when they nest actions. That stage evaluated `with:` before earlier steps ran, so an input like `${{ fromJSON(steps.meta.outputs.json).v }}` failed the job.
- `ports` on a job container are published, they were ignored while service ports worked.
- Dockerfile action build output reaches the job log. It was logged at debug and dropped, so a failing `RUN` showed only the final error.
- Local Docker actions honor their `.dockerignore`, as `docker build` does.
- Cancelling or timing out a host-mode step sends SIGINT, then SIGTERM after 7.5 seconds and SIGKILL after 2.5 more, as GitHub's runner does, so `trap` handlers and shutdown hooks run.
- `.sh` job hooks fall back to `sh` where bash is missing, and `.ps1` hooks to `powershell` where pwsh is missing, as on GitHub.

_Written by Claude (Opus 5.5)._

Reviewed-on: https://gitea.com/gitea/runner/pulls/1413
Reviewed-by: bircni <[email protected]>
Co-authored-by: silverwind <[email protected]>

act/container/docker_images_test.go

@@ -38,7 +38,7 @@ func loadScratchImage(t *testing.T, platform string) string {
 	response, err := cli.ImageLoad(t.Context(), &archive)
 	require.NoError(t, err)
 	defer response.Close()
-	require.NoError(t, logDockerResponse(common.Logger(t.Context()), response, false))
+	require.NoError(t, logDockerResponse(common.Logger(t.Context()), response, common.Logger(t.Context()).Debugf))
 	t.Cleanup(func() {
 		_, _ = cli.ImageRemove(context.WithoutCancel(t.Context()), tag, mobyclient.ImageRemoveOptions{Force: true})
 	})