fix(review): fix slice preallocation bug and remove redundant assignment

In answer.go, make([]string, len(...)) pre-fills with empty strings
before appending, producing a slice like ["", "", "composer", "pip"].
Use capacity instead of length.

In stack.go, the Symfony non-interactive case redundantly sets
answers.Stack to GenericStack — it was already set before the switch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pjcdawkins

internal/question/models/answer.go

@@ -113,7 +113,7 @@ func (a *Answers) ToUserInput() *platformifier.UserInput {
 		locations[key] = value
 	}
 
-	dependencyManagers := make([]string, len(a.DependencyManagers))
+	dependencyManagers := make([]string, 0, len(a.DependencyManagers))
 	for _, dm := range a.DependencyManagers {
 		dependencyManagers = append(dependencyManagers, dm.String())
 	}

internal/question/stack.go

@@ -69,7 +69,6 @@ func (q *Stack) Ask(ctx context.Context) error {
 		return nil
 	case platformifier.Symfony:
 		if answers.NoInteraction {
-			answers.Stack = models.GenericStack
 			return nil
 		}
 		// Interactive: offer Symfony CLI below.