refactor: adopt PathRegistry in queue filesystem_queue.go

Update internal/queue/filesystem_queue.go to use centralized PathRegistry:

Changes:
- Add import for internal/config package
- Update NewFilesystemQueue to use config.FromEnv() for directory creation
- Replace os.MkdirAll with paths.EnsureDir() for all queue directories:
  - pending/entries
  - running
  - finished
  - failed

Benefits:
- Consistent directory creation via PathRegistry
- Centralized path management for queue storage
- Better error handling for directory creation

internal/queue/filesystem_queue.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/jfraeys/fetch_ml/internal/config"
 	"github.com/jfraeys/fetch_ml/internal/domain"
 )
 
@@ -38,11 +39,15 @@ func NewFilesystemQueue(root string) (*FilesystemQueue, error) {
 		return nil, fmt.Errorf("filesystem queue root is required")
 	}
 	root = filepath.Clean(root)
-	if err := os.MkdirAll(filepath.Join(root, "pending", "entries"), 0750); err != nil {
+
+	// Use PathRegistry for consistent directory creation
+	paths := config.FromEnv()
+
+	if err := paths.EnsureDir(filepath.Join(root, "pending", "entries")); err != nil {
 		return nil, err
 	}
 	for _, d := range []string{"running", "finished", "failed"} {
-		if err := os.MkdirAll(filepath.Join(root, d), 0750); err != nil {
+		if err := paths.EnsureDir(filepath.Join(root, d)); err != nil {
 			return nil, err
 		}
 	}