refactor: adopt PathRegistry in jupyter workspace_metadata.go

Update internal/jupyter/workspace_metadata.go to use centralized PathRegistry:

Changes:
- Add import for internal/config package
- Update saveMetadata() to use config.FromEnv() for directory creation
- Replace os.MkdirAll with paths.EnsureDir() for metadata directory

Benefits:
- Consistent directory creation via PathRegistry
- Centralized path management for workspace metadata
- Better error handling for directory creation

internal/jupyter/workspace_metadata.go

@@ -8,6 +8,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/jfraeys/fetch_ml/internal/config"
 	"github.com/jfraeys/fetch_ml/internal/logging"
 )
 
@@ -318,10 +319,11 @@ func (wmm *WorkspaceMetadataManager) loadMetadata() error {
 	return nil
 }
 
-// saveMetadata saves metadata to disk
+// saveMetadata saves metadata to disk using PathRegistry
 func (wmm *WorkspaceMetadataManager) saveMetadata() error {
-	// Ensure directory exists
-	if err := os.MkdirAll(filepath.Dir(wmm.dataFile), 0750); err != nil {
+	// Use PathRegistry for consistent directory creation
+	paths := config.FromEnv()
+	if err := paths.EnsureDir(filepath.Dir(wmm.dataFile)); err != nil {
 		return fmt.Errorf("failed to create metadata directory: %w", err)
 	}