refactor: drop logrus and other direct dependencies (#1319)

After https://gitea.com/gitea/runner/pulls/1304, logrus stayed only to forward logs from docker/cli and moby/go-archive. The runner used a small part of those: volume parsing, the build context tar, the `ssh://` connection and registry credentials. Own code that matches them replaces them, so logrus leaves the module graph. docker/cli stays for its logrus-free `opts` and `connhelper/ssh` packages.

Other dependencies that the standard library or existing ones cover go too: mergo, httprouter (replaced by `http.ServeMux`), retry-go, go-isatty, go-selinux, container-device-interface, gotest.tools and go-cmp (replaced by testify). The binary shrinks by 5%.

Behaviour differences:

1. An unreadable file in a build context is skipped with a warning, where go-archive left a truncated tar.
2. Build contexts no longer carry `security.capability` xattrs.
3. The cache and artifact servers answer HEAD on GET routes, and no longer redirect trailing slashes or answer OPTIONS.

*Written by Claude.*

---------

Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1319
Reviewed-by: bircni <[email protected]>
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: silverwind <[email protected]>

act/container/docker_build_test.go

@@ -0,0 +1,49 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build !(WITHOUT_DOCKER || !(linux || darwin || windows || netbsd))
+
+package container
+
+import (
+	"archive/tar"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestCreateBuildContextFollowsDockerignoreAndSymlinkedRootButKeepsDockerfile(t *testing.T) {
+	dir := t.TempDir()
+	for name, content := range map[string]string{
+		".dockerignore": "*.log\nbuild\n!build/keep.txt\nDockerfile", "Dockerfile": "FROM scratch", "a.txt": "a",
+		"a.log": "log", "build/drop.txt": "drop", "build/keep.txt": "keep",
+	} {
+		require.NoError(t, os.MkdirAll(filepath.Join(dir, filepath.Dir(name)), 0o755))
+		require.NoError(t, os.WriteFile(filepath.Join(dir, name), []byte(content), 0o644))
+	}
+	require.NoError(t, os.Mkdir(filepath.Join(dir, "empty"), 0o755))
+
+	contexts := []string{dir}
+	if link := filepath.Join(t.TempDir(), "link"); os.Symlink(dir, link) == nil {
+		contexts = append(contexts, link+string(filepath.Separator))
+	}
+
+	for _, contextDir := range contexts {
+		buildContext, err := createBuildContext(t.Context(), contextDir, "Dockerfile")
+		require.NoError(t, err)
+		var names []string
+		for reader := tar.NewReader(buildContext); ; {
+			header, err := reader.Next()
+			if err == io.EOF {
+				break
+			}
+			require.NoError(t, err)
+			names = append(names, header.Name)
+		}
+		require.NoError(t, buildContext.Close())
+		require.Equal(t, []string{".dockerignore", "a.txt", "build/keep.txt", "empty/", "Dockerfile"}, names, contextDir)
+	}
+}