refactor: clean up verbose and redundant comments

Trim or remove comments that:
- State the obvious (function names already convey purpose)
- Repeat what the code clearly shows
- Are excessively long without adding value

Keep comments that explain *why*, not *what*.

internal/engines/factory.go

@@ -24,9 +24,8 @@ import (
 	"github.com/metamorphosis-dev/kafka/internal/config"
 )
 
-// NewDefaultPortedEngines returns the starter set of Go-native engines.
-// The service can swap/extend this registry later as more engines are ported.
-// If cfg is nil, falls back to reading API keys from environment variables.
+// NewDefaultPortedEngines returns the Go-native engine registry.
+// If cfg is nil, API keys fall back to environment variables.
 func NewDefaultPortedEngines(client *http.Client, cfg *config.Config) map[string]Engine {
 	if client == nil {
 		client = &http.Client{Timeout: 10 * time.Second}