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.

testdata/yaml-fixtures/actions/javascript/node16.yml

@@ -0,0 +1,23 @@
+name: 'Node.js 16 Action'
+description: 'JavaScript action running on Node.js 16'
+inputs:
+  script-path:
+    description: 'Path to the script to execute'
+    required: true
+  args:
+    description: 'Arguments to pass to the script'
+    required: false
+    default: ''
+outputs:
+  exit-code:
+    description: 'Exit code of the script'
+  stdout:
+    description: 'Standard output from the script'
+runs:
+  using: 'node16'
+  main: 'dist/index.js'
+  pre: 'dist/setup.js'
+  post: 'dist/cleanup.js'
+branding:
+  icon: 'terminal'
+  color: 'green'