Adds initial gitlocal CLI and core functionality

Introduces the `gitlocal` command-line tool for managing nested Git repositories.

Includes the following main commands:
- `convert`: Renames `.git` to `.gitlocal`, allowing a parent repository to ignore the converted child repository. Supports recursive scanning and dry-run options. Tracks converted repositories in a global configuration.
- `revert`: Restores `.gitlocal` to `.git`. Includes an option to revert all tracked repositories.
- `status`: Displays a list of all repositories currently tracked by `gitlocal`, showing their path, conversion time, and original remote/branch.

Establishes internal modules for Git operations, configuration management, and recursive repository scanning.
Adds a comprehensive test suite covering core command logic and utility functions.
Initializes Go module and basic project `.gitignore`.

internal/testutil/testutil.go

@@ -0,0 +1,158 @@
+package testutil
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+// CreateTempGitRepo creates a temporary directory with a git repository
+func CreateTempGitRepo(t *testing.T) string {
+	t.Helper()
+
+	dir := t.TempDir()
+
+	// Initialize git repo
+	cmd := exec.Command("git", "init")
+	cmd.Dir = dir
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("failed to init git repo: %v", err)
+	}
+
+	// Configure git user for the test repo
+	configName := exec.Command("git", "config", "user.name", "Test User")
+	configName.Dir = dir
+	if err := configName.Run(); err != nil {
+		t.Fatalf("failed to configure git user.name: %v", err)
+	}
+
+	configEmail := exec.Command("git", "config", "user.email", "test@example.com")
+	configEmail.Dir = dir
+	if err := configEmail.Run(); err != nil {
+		t.Fatalf("failed to configure git user.email: %v", err)
+	}
+
+	// Create initial commit
+	readmePath := filepath.Join(dir, "README.md")
+	if err := os.WriteFile(readmePath, []byte("# Test Repo\n"), 0644); err != nil {
+		t.Fatalf("failed to create README: %v", err)
+	}
+
+	add := exec.Command("git", "add", "README.md")
+	add.Dir = dir
+	if err := add.Run(); err != nil {
+		t.Fatalf("failed to git add: %v", err)
+	}
+
+	commit := exec.Command("git", "commit", "-m", "Initial commit")
+	commit.Dir = dir
+	if err := commit.Run(); err != nil {
+		t.Fatalf("failed to git commit: %v", err)
+	}
+
+	return dir
+}
+
+// CreateTempGitRepoWithRemote creates a temporary git repo with a remote URL configured
+func CreateTempGitRepoWithRemote(t *testing.T, remoteURL string) string {
+	t.Helper()
+
+	dir := CreateTempGitRepo(t)
+
+	// Add remote
+	cmd := exec.Command("git", "remote", "add", "origin", remoteURL)
+	cmd.Dir = dir
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("failed to add git remote: %v", err)
+	}
+
+	return dir
+}
+
+// CreateTempGitRepoWithBranch creates a temporary git repo on a specific branch
+func CreateTempGitRepoWithBranch(t *testing.T, branch string) string {
+	t.Helper()
+
+	dir := CreateTempGitRepo(t)
+
+	// Create and checkout branch
+	cmd := exec.Command("git", "checkout", "-b", branch)
+	cmd.Dir = dir
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("failed to create branch: %v", err)
+	}
+
+	return dir
+}
+
+// CreateNestedRepoStructure creates a directory structure with nested git repos
+// Returns the root directory path
+func CreateNestedRepoStructure(t *testing.T) (rootDir string, nestedDirs []string) {
+	t.Helper()
+
+	rootDir = CreateTempGitRepo(t)
+
+	// Create nested repos
+	nested1 := filepath.Join(rootDir, "project1")
+	if err := os.MkdirAll(nested1, 0755); err != nil {
+		t.Fatalf("failed to create nested dir: %v", err)
+	}
+	initGit(t, nested1)
+
+	nested2 := filepath.Join(rootDir, "subdir", "project2")
+	if err := os.MkdirAll(nested2, 0755); err != nil {
+		t.Fatalf("failed to create nested dir: %v", err)
+	}
+	initGit(t, nested2)
+
+	nested3 := filepath.Join(rootDir, "subdir", "deep", "project3")
+	if err := os.MkdirAll(nested3, 0755); err != nil {
+		t.Fatalf("failed to create nested dir: %v", err)
+	}
+	initGit(t, nested3)
+
+	return rootDir, []string{nested1, nested2, nested3}
+}
+
+// initGit initializes a git repo in the given directory
+func initGit(t *testing.T, dir string) {
+	t.Helper()
+
+	cmd := exec.Command("git", "init")
+	cmd.Dir = dir
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("failed to init git repo: %v", err)
+	}
+
+	// Configure git user
+	configName := exec.Command("git", "config", "user.name", "Test User")
+	configName.Dir = dir
+	if err := configName.Run(); err != nil {
+		t.Fatalf("failed to configure git user.name: %v", err)
+	}
+
+	configEmail := exec.Command("git", "config", "user.email", "test@example.com")
+	configEmail.Dir = dir
+	if err := configEmail.Run(); err != nil {
+		t.Fatalf("failed to configure git user.email: %v", err)
+	}
+
+	// Create initial commit
+	readmePath := filepath.Join(dir, "README.md")
+	if err := os.WriteFile(readmePath, []byte("# Test\n"), 0644); err != nil {
+		t.Fatalf("failed to create README: %v", err)
+	}
+
+	add := exec.Command("git", "add", "README.md")
+	add.Dir = dir
+	if err := add.Run(); err != nil {
+		t.Fatalf("failed to git add: %v", err)
+	}
+
+	commit := exec.Command("git", "commit", "-m", "Initial commit")
+	commit.Dir = dir
+	if err := commit.Run(); err != nil {
+		t.Fatalf("failed to git commit: %v", err)
+	}
+}