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_pull_test.go

@@ -95,15 +95,16 @@ func TestIsPinnedImage(t *testing.T) {
 // The pull path reports a failure the daemon sent mid-stream, so it must carry the reason
 // whichever of the two shapes the daemon used.
 func TestLogDockerResponseError(t *testing.T) {
-	logger := logging.New(logtest.New())
+	logger, hook := logtest.NewLogger()
 	streamErr := func(line string) error {
-		return logDockerResponse(logger, io.NopCloser(strings.NewReader(line)), false)
+		return logDockerResponse(logger, io.NopCloser(strings.NewReader(line)), logger.Infof)
 	}
 	require.EqualError(t, streamErr(`{"error":"toomanyrequests: rate limit exceeded"}`), "toomanyrequests: rate limit exceeded")
 	require.EqualError(t, streamErr(`{"errorDetail":{"message":"unexpected EOF"}}`), "unexpected EOF")
 	require.NoError(t, streamErr(`{"status":"Downloading"}`))
 	require.NoError(t, streamErr(`{"stream":"`+strings.Repeat("x", 70000)+`"}`))
+	assert.Equal(t, logging.LevelInfo, hook.LastRecord().Level)
 	require.ErrorIs(t, logDockerResponse(logger, io.NopCloser(io.MultiReader(
 		strings.NewReader(`{"status":"Downloading"}`+"\n"), iotest.ErrReader(io.ErrUnexpectedEOF),
-	)), false), io.ErrUnexpectedEOF)
+	)), logger.Infof), io.ErrUnexpectedEOF)
 }