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/cache/cache.go

@@ -27,6 +27,7 @@ type Cache struct {
 	ticker     *time.Ticker     // Cleanup ticker
 	done       chan bool        // Cleanup shutdown
 	defaultTTL time.Duration    // Default TTL for entries
+	saveWG     sync.WaitGroup   // Wait group for pending save operations
 }
 
 // Config represents cache configuration.
@@ -58,7 +59,7 @@ func NewCache(config *Config) (*Cache, error) {
 	}
 
 	// Ensure cache directory exists
-	if err := os.MkdirAll(filepath.Dir(cacheDir), 0755); err != nil {
+	if err := os.MkdirAll(filepath.Dir(cacheDir), 0750); err != nil { // #nosec G301 -- cache directory permissions
 		return nil, fmt.Errorf("failed to create cache directory: %w", err)
 	}
 
@@ -188,6 +189,9 @@ func (c *Cache) Close() error {
 	default:
 	}
 
+	// Wait for any pending async save operations to complete
+	c.saveWG.Wait()
+
 	// Save final state to disk
 	return c.saveToDisk()
 }
@@ -224,7 +228,7 @@ func (c *Cache) cleanup() {
 func (c *Cache) loadFromDisk() error {
 	cacheFile := filepath.Join(c.path, "cache.json")
 
-	data, err := os.ReadFile(cacheFile)
+	data, err := os.ReadFile(cacheFile) // #nosec G304 -- cache file path constructed internally
 	if err != nil {
 		if os.IsNotExist(err) {
 			return nil // No cache file is fine
@@ -257,7 +261,7 @@ func (c *Cache) saveToDisk() error {
 	}
 
 	cacheFile := filepath.Join(c.path, "cache.json")
-	if err := os.WriteFile(cacheFile, jsonData, 0644); err != nil {
+	if err := os.WriteFile(cacheFile, jsonData, 0600); err != nil { // #nosec G306 -- cache file permissions
 		return fmt.Errorf("failed to write cache file: %w", err)
 	}
 
@@ -267,7 +271,9 @@ func (c *Cache) saveToDisk() error {
 // saveToDiskAsync saves the cache to disk asynchronously.
 // Cache save failures are non-critical and silently ignored.
 func (c *Cache) saveToDiskAsync() {
+	c.saveWG.Add(1)
 	go func() {
+		defer c.saveWG.Done()
 		_ = c.saveToDisk() // Ignore errors - cache save failures are non-critical
 	}()
 }

internal/cache/cache_test.go

@@ -313,6 +313,43 @@ func TestCache_Clear(t *testing.T) {
 	}
 }
 
+func TestCache_Delete(t *testing.T) {
+	tmpDir, cleanup := testutil.TempDir(t)
+	defer cleanup()
+
+	cache := createTestCache(t, tmpDir)
+	defer func() { _ = cache.Close() }()
+
+	// Add some data
+	_ = cache.Set("key1", "value1")
+	_ = cache.Set("key2", "value2")
+	_ = cache.Set("key3", "value3")
+
+	// Verify data exists
+	_, exists := cache.Get("key1")
+	if !exists {
+		t.Fatal("expected key1 to exist before delete")
+	}
+
+	// Delete specific key
+	cache.Delete("key1")
+
+	// Verify deleted key is gone but others remain
+	_, exists1 := cache.Get("key1")
+	_, exists2 := cache.Get("key2")
+	_, exists3 := cache.Get("key3")
+
+	if exists1 {
+		t.Error("expected key1 to be deleted")
+	}
+	if !exists2 || !exists3 {
+		t.Error("expected key2 and key3 to still exist")
+	}
+
+	// Test deleting non-existent key (should not panic)
+	cache.Delete("nonexistent")
+}
+
 func TestCache_Stats(t *testing.T) {
 	tmpDir, cleanup := testutil.TempDir(t)
 	defer cleanup()
@@ -320,6 +357,9 @@ func TestCache_Stats(t *testing.T) {
 	cache := createTestCache(t, tmpDir)
 	defer func() { _ = cache.Close() }()
 
+	// Ensure cache starts clean
+	_ = cache.Clear()
+
 	// Add some data
 	_ = cache.Set("key1", "value1")
 	_ = cache.Set("key2", "larger-value-with-more-content")