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/composite/basic.yml

@@ -0,0 +1,25 @@
+name: 'Basic Composite Action'
+description: 'A simple composite action with basic steps'
+inputs:
+  working-directory:
+    description: 'Working directory for commands'
+    required: false
+    default: '.'
+outputs:
+  status:
+    description: 'Overall status of the workflow'
+    value: ${{ steps.final.outputs.status }}
+runs:
+  using: 'composite'
+  steps:
+    - name: Setup
+      run: echo "Setting up environment"
+      shell: bash
+    - name: Main task
+      run: echo "Running main task in ${{ inputs.working-directory }}"
+      shell: bash
+      working-directory: ${{ inputs.working-directory }}
+    - name: Final step
+      id: final
+      run: echo "status=success" >> $GITHUB_OUTPUT
+      shell: bash