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.

Makefile

@@ -1,84 +1,113 @@
-.PHONY: test lint run example clean readme config-verify security vulncheck audit snyk trivy gitleaks \
+.PHONY: help test lint run example clean readme config-verify security vulncheck audit snyk trivy gitleaks \
 	editorconfig editorconfig-fix format
 
-all: test lint
+all: help
 
-test:
+help: ## Show this help message
+	@echo "GitHub Action README Generator - Available Make Targets:"
+	@echo ""
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | \
+		awk 'BEGIN {FS = ":.*?## "}; {printf "  \033[36m%-20s\033[0m %s\n", $$1, $$2}'
+	@echo ""
+	@echo "Common workflows:"
+	@echo "  make test lint     # Run tests and linting"
+	@echo "  make format        # Format code and fix EditorConfig issues"
+	@echo "  make security      # Run all security scans"
+
+test: ## Run all tests
 	go test ./...
 
-lint: editorconfig
+lint: format ## Run linter (after formatting)
 	golangci-lint run || true
 
-config-verify:
+config-verify: ## Verify golangci-lint configuration
 	golangci-lint config verify --verbose
 
-run:
+run: ## Run the application
 	go run .
 
-example:
+example: ## Generate example README
 	go run . gen --config config.yaml --output-format=md
 
-readme:
+readme: ## Generate project README
 	go run . gen --config config.yaml --output-format=md
 
-clean:
+clean: ## Clean build artifacts
 	rm -rf dist/
 
 # Code formatting and EditorConfig targets
-format: editorconfig-fix
+format: editorconfig-fix ## Format code and fix EditorConfig issues
 	@echo "Running all formatters..."
 	@command -v gofmt >/dev/null 2>&1 && gofmt -w -s . || echo "gofmt not available"
 	@command -v goimports >/dev/null 2>&1 && \
 		goimports -w -local github.com/ivuorinen/gh-action-readme . || \
 		echo "goimports not available"
 
-editorconfig:
+editorconfig: ## Check EditorConfig compliance
 	@echo "Checking EditorConfig compliance..."
 	@command -v eclint >/dev/null 2>&1 || \
 		{ echo "Please install eclint: npm install -g eclint"; exit 1; }
-	@echo "Checking key files for EditorConfig compliance..."
-	eclint check Makefile .github/workflows/*.yml main.go internal/**/*.go *.md .goreleaser.yaml
+	@echo "Checking files for EditorConfig compliance..."
+	@find . -type f \( \
+		-name "*.go" -o \
+		-name "*.yml" -o \
+		-name "*.yaml" -o \
+		-name "*.json" -o \
+		-name "*.md" -o \
+		-name "Makefile" -o \
+		-name "*.tmpl" -o \
+		-name "*.adoc" -o \
+		-name "*.sh" \
+	\) -not -path "./.*" -not -path "./gh-action-readme" -not -path "./coverage*" \
+		-not -path "./testutil.test" -not -path "./test_*" | \
+		xargs eclint check
 
-editorconfig-fix:
+editorconfig-fix: ## Fix EditorConfig violations
 	@echo "Fixing EditorConfig violations..."
 	@command -v eclint >/dev/null 2>&1 || \
 		{ echo "Please install eclint: npm install -g eclint"; exit 1; }
-	@echo "Fixing key files for EditorConfig compliance..."
-	eclint fix Makefile .github/workflows/*.yml main.go internal/**/*.go *.md .goreleaser.yaml
-
-editorconfig-check:
-	@echo "Running editorconfig-checker..."
-	@command -v editorconfig-checker >/dev/null 2>&1 || \
-		{ echo "Please install editorconfig-checker: npm install -g editorconfig-checker"; exit 1; }
-	editorconfig-checker
+	@echo "Fixing files for EditorConfig compliance..."
+	@find . -type f \( \
+		-name "*.go" -o \
+		-name "*.yml" -o \
+		-name "*.yaml" -o \
+		-name "*.json" -o \
+		-name "*.md" -o \
+		-name "Makefile" -o \
+		-name "*.tmpl" -o \
+		-name "*.adoc" -o \
+		-name "*.sh" \
+	\) -not -path "./.*" -not -path "./gh-action-readme" -not -path "./coverage*" \
+		-not -path "./testutil.test" -not -path "./test_*" | \
+		xargs eclint fix
 
 # Security targets
-security: vulncheck snyk trivy gitleaks
+security: vulncheck snyk trivy gitleaks ## Run all security scans
 	@echo "All security scans completed"
 
-vulncheck:
+vulncheck: ## Run Go vulnerability check
 	@echo "Running Go vulnerability check..."
 	@command -v govulncheck >/dev/null 2>&1 || \
 		{ echo "Installing govulncheck..."; go install golang.org/x/vuln/cmd/govulncheck@latest; }
 	govulncheck ./...
 
-audit: vulncheck
+audit: vulncheck ## Run comprehensive security audit
 	@echo "Running comprehensive security audit..."
 	go list -json -deps ./... | jq -r '.Module | select(.Path != null) | .Path + "@" + .Version' | sort -u
 
-snyk:
+snyk: ## Run Snyk security scan
 	@echo "Running Snyk security scan..."
 	@command -v snyk >/dev/null 2>&1 || \
 		{ echo "Please install Snyk CLI: npm install -g snyk"; exit 1; }
 	snyk test --file=go.mod --package-manager=gomodules
 
-trivy:
+trivy: ## Run Trivy filesystem scan
 	@echo "Running Trivy filesystem scan..."
 	@command -v trivy >/dev/null 2>&1 || \
 		{ echo "Please install Trivy: https://aquasecurity.github.io/trivy/"; exit 1; }
 	trivy fs . --severity HIGH,CRITICAL
 
-gitleaks:
+gitleaks: ## Run gitleaks secrets detection
 	@echo "Running gitleaks secrets detection..."
 	@command -v gitleaks >/dev/null 2>&1 || \
 		{ echo "Please install gitleaks: https://github.com/gitleaks/gitleaks"; exit 1; }