feat(gui): allow changing workflow access level

[seongjinyoon]

What changes were proposed in this PR?

Previously, when a user was given access to a workflow, the access level (READ/WRITE) could not be changed directly. Users had to revoke access and re-add with the new level. This PR adds the ability for users with write access to change the access level of other users via a dropdown.

Frontend (share-access.component.ts / share-access.component.html):

• Added hasWriteAccess that checks write access.
• Added changeAccessLevel() method with confirmation warning when a user downgrades their own access from WRITE to READ.
• Dropdown disabled for users without write access.

Backend (WorkflowAccessResource.scala):

• Modified grantAccess endpoint to allow users with WRITE access to modify their own access level

Behavior:

• Users with WRITE access can change other users' access levels via dropdown
• Users with WRITE access can downgrade their own access to READ
• Owner's access cannot be changed

Demo:

Screen.Recording.2026-01-14.at.3.51.53.PM.mov

Any related issues, documentation, discussions?

No

How was this PR tested?

Manually tested.

Was this PR authored or co-authored using generative AI tooling?

Revised with Claude Code.

[seongjinyoon]

@Xiao-zhen-Liu Can you review this PR please?

[chenlica]

@seongjinyoon Thanks. Is it possible to add test cases?