[feat] Allow editing data references of existing metadata documents

[das-Abroxas]

Goal

Allow users to modify the data references of an existing RO-Crate metadata document. Data references are currently configurable during creation but missing from the edit dialog.

Workplan

1. Add data-reference management to the RO-Crate edit dialog
2. Persist the changes through the existing update workflow

Definition of Done

• Data references can be added, modified, and removed
• Updated references are persisted correctly

Test Concept

Create an RO-Crate with data references, modify them through the edit dialog, and verify the changes after reopening the document.

Risks

Changes to data references may leave invalid or dangling references within the RO-Crate document.