[Reviewer UI] Let reviewers read, save and submit their review through the review assignment API

[blesildaramirez]

Follow-up to #12534 - the Vue migration for the reviewer's Step 3 needs to use the review assignment API instead of the legacy reviewer/saveStep handler. This is needed for #12534 to move the reviewer Step 3 UI fully to the API.

The API already supports editors through:

GET/PUT submissions/{submissionId}/reviewAssignments/{reviewAssignmentId}/review

and:

GET submissions/{submissionId}/reviewAssignments/{reviewAssignmentId}

We need to make these endpoints available to reviewers for their own review assignment, while keeping the existing editor-only actions protected.

Requirements

Read

Reviewers should be able to:

• Get their review assignment
• Get their review, including form responses/comments and recommendation

The assignment response should only expose information relevant to the reviewer.

Save for later

The reviewer should be able to save an incomplete review without completing it.

This should save the current responses/comments and recommendation, but should not:

• Complete the review or set dateCompleted
• Advance the review step
• Notify editors
• Remove the reviewer's task

Required fields should not prevent a "Save for later".

Submit

Submitting should perform the normal review completion flow:

• Validate the review
• Save the review
• Mark it as completed and advance the step
• Notify the editors
• Remove the reviewer's task
• Finalize reviewer access

Access

A reviewer should only be able to access and modify their own review assignment. Reviewers should not gain access to the existing editor-only review assignment actions.

Completed reviews should remain read-only to the reviewer, while editors can continue to modify them.