refactor: major codebase improvements and test framework overhaul

This commit represents a comprehensive refactoring of the codebase focused on
improving code quality, testability, and maintainability.

Key improvements:
- Implement dependency injection and interface-based architecture
- Add comprehensive test framework with fixtures and test suites
- Fix all linting issues (errcheck, gosec, staticcheck, goconst, etc.)
- Achieve full EditorConfig compliance across all files
- Replace hardcoded test data with proper fixture files
- Add configuration loader with hierarchical config support
- Improve error handling with contextual information
- Add progress indicators for better user feedback
- Enhance Makefile with help system and improved editorconfig commands
- Consolidate constants and remove deprecated code
- Strengthen validation logic for GitHub Actions
- Add focused consumer interfaces for better separation of concerns

Testing improvements:
- Add comprehensive integration tests
- Implement test executor pattern for better test organization
- Create extensive YAML fixture library for testing
- Fix all failing tests and improve test coverage
- Add validation test fixtures to avoid embedded YAML in Go files

Build and tooling:
- Update Makefile to show help by default
- Fix editorconfig commands to use eclint properly
- Add comprehensive help documentation to all make targets
- Improve file selection patterns to avoid glob errors

This refactoring maintains backward compatibility while significantly
improving the internal architecture and developer experience.

internal/template.go

@@ -12,6 +12,7 @@ import (
 	"github.com/ivuorinen/gh-action-readme/internal/cache"
 	"github.com/ivuorinen/gh-action-readme/internal/dependencies"
 	"github.com/ivuorinen/gh-action-readme/internal/git"
+	"github.com/ivuorinen/gh-action-readme/internal/validation"
 )
 
 const (
@@ -45,10 +46,6 @@ type TemplateData struct {
 	Dependencies []dependencies.Dependency `json:"dependencies,omitempty"`
 }
 
-// GitInfo contains Git repository information for templates.
-// Note: GitInfo struct removed - using git.RepoInfo instead to avoid duplication
-// Note: Dependency struct is now defined in internal/dependencies package
-
 // templateFuncs returns a map of custom template functions.
 func templateFuncs() template.FuncMap {
 	return template.FuncMap{
@@ -115,19 +112,19 @@ func isValidOrgRepo(org, repo string) bool {
 // formatVersion ensures version has proper @ prefix.
 func formatVersion(version string) string {
 	version = strings.TrimSpace(version)
-	if version != "" && !strings.HasPrefix(version, "@") {
-		return "@" + version
-	}
 	if version == "" {
 		return "@v1"
 	}
+	if !strings.HasPrefix(version, "@") {
+		return "@" + version
+	}
 	return version
 }
 
 // buildUsesString constructs the uses string with optional action name.
 func buildUsesString(td *TemplateData, org, repo, version string) string {
 	if td.Name != "" {
-		actionName := strings.ToLower(strings.ReplaceAll(strings.TrimSpace(td.Name), " ", "-"))
+		actionName := validation.SanitizeActionName(td.Name)
 		if actionName != "" && actionName != repo {
 			return fmt.Sprintf("%s/%s/%s%s", org, repo, actionName, version)
 		}
@@ -225,7 +222,7 @@ func RenderReadme(action any, opts TemplateOptions) (string, error) {
 		return "", err
 	}
 	var tmpl *template.Template
-	if opts.Format == "html" {
+	if opts.Format == OutputFormatHTML {
 		tmpl, err = template.New("readme").Funcs(templateFuncs()).Parse(string(tmplContent))
 		if err != nil {
 			return "", err