Complete remaining RBAC Creator pattern for guarded entities

Remaining RBAC Creator pattern tasks carried over from BA-2838 (Apply RBAC Creator and Purger pattern), which has been completed for the majority of guarded entities.

The following entities still need RBAC Creator pattern applied:

- Agent (BA-3701)

- Storage Volume (BA-3702)

- ProjectFairShare (BA-5076)

- UserFairShare (BA-5077)

Reference:

- BEP-1048: RBAC Entity Relationship Model (guarded entity list)

- BA-2838: Original epic (completed)

JIRA Issue: BA-5676

Start by reading BEP-1048 for the guarded-entity relationships and BA-2838 for the completed RBAC Creator pattern. Compare the remaining Agent, Storage Volume, ProjectFairShare, and UserFairShare entities with the entities already covered; done means all four consistently follow the Creator pattern.

Written by the indexing model from the issue text.