Update storage host permission UI per CoreDev's permission model direction

## Summary

Storage host permission **editing** in WebUI is already shipped (FR-2969 epic: detail drawer + Permissions tab, migrated from Control Panel). However, how storage host permissions will ultimately be organized on the backend side (e.g. the relationship between legacy `allowed_vfolder_hosts` on domain/project/keypair-resource-policy and the newer permission model such as RBAC / `myStorageHostPermissions`) is still an open question on the CoreDev side.

CoreDev agreed to decide the direction and share it with the frontend team. Once the direction is finalized, the WebUI storage host permission UI (and related merge/union logic) should be updated accordingly.

## Blocked by

- Backend/CoreDev decision on the storage host permission model direction (promised to be shared after the direction is settled).

## Related

- FR-2969 — Migrate storage host permission management from Control Panel to WebUI (Done)
- FR-3010 — Project Folder / User Folder permission tabs (Done)
- FR-3229 — Migrate waterfall allowed_vfolder_hosts merge to myStorageHostPermissions (In Progress)

JIRA Issue: FR-3381

Start by reviewing FR-3229 and the existing storage host permission UI migrated under FR-2969. Wait for the CoreDev decision on the backend permission model, then update the WebUI and related merge/union logic to match; done means the UI reflects the finalized direction.

Written by the indexing model from the issue text.