feat: initial commit of Git Automation CLI

- Add comprehensive Git workflow automation tools
- Include branch management utilities
- Add commit helpers with conventional commit support
- Implement GitHub integration for PR management
- Add configuration management system
- Include comprehensive test coverage
- Add professional documentation and examples

internal/util/env.go

@@ -0,0 +1,13 @@
+package util
+
+import (
+	"os"
+)
+
+func GetenvOrDefault(key, def string) string {
+	v := os.Getenv(key)
+	if v == "" {
+		return def
+	}
+	return v
+}

internal/util/env_test.go

@@ -0,0 +1,44 @@
+package util
+
+import (
+	"os"
+	"testing"
+)
+
+func TestGetenvOrDefault(t *testing.T) {
+	// Save original environment variable value
+	originalValue, exists := os.LookupEnv("TEST_ENV_VAR")
+	
+	// Clean up after test
+	defer func() {
+		if exists {
+			os.Setenv("TEST_ENV_VAR", originalValue)
+		} else {
+			os.Unsetenv("TEST_ENV_VAR")
+		}
+	}()
+	
+	// Test 1: Environment variable is not set
+	os.Unsetenv("TEST_ENV_VAR")
+	result := GetenvOrDefault("TEST_ENV_VAR", "default")
+	expected := "default"
+	if result != expected {
+		t.Errorf("Expected '%s', got '%s'", expected, result)
+	}
+	
+	// Test 2: Environment variable is set to empty string
+	os.Setenv("TEST_ENV_VAR", "")
+	result = GetenvOrDefault("TEST_ENV_VAR", "default")
+	expected = "default"
+	if result != expected {
+		t.Errorf("Expected '%s', got '%s'", expected, result)
+	}
+	
+	// Test 3: Environment variable is set to a value
+	os.Setenv("TEST_ENV_VAR", "test_value")
+	result = GetenvOrDefault("TEST_ENV_VAR", "default")
+	expected = "test_value"
+	if result != expected {
+		t.Errorf("Expected '%s', got '%s'", expected, result)
+	}
+}