## Summary
Follow-up to #20260. The `MorphRelationManyToOneFieldDisplay` component
(used for polymorphic MANY_TO_ONE relations) was missing the FK-presence
check that `RelationToOneFieldDisplay` already has.
When RLS hides a related record (e.g., a Rocket with a policy filtering
by name), the API response contains a populated FK
(`polymorphicOwnerRocketId`) but a `null` relation object. The component
was rendering an empty cell instead of the "Not shared" lock icon.
**Fix:**
- In `useMorphRelationToOneFieldDisplay`, read the record from the store
and check if any morph relation FK field is populated while the relation
value is null
- In `MorphRelationManyToOneFieldDisplay`, render
`<ForbiddenFieldDisplay />` when that condition is true
| Scenario | FK in response | Relation object | Frontend display |
|----------|---------------|-----------------|-----------------|
| Live record | "abc" | `{ id: "abc", ... }` | Record chip |
| Soft-deleted record | null | null | Empty cell |
| RLS-hidden record | "abc" | null | "Not shared" |
## Test plan
- Create a polymorphic MANY_TO_ONE relation (e.g., Pet → Rocket)
- Add an RLS policy on the target object (e.g., Rocket name contains
"Starship")
- Verify the morph relation field shows "Not shared" (lock icon) for
RLS-hidden records
- Verify live records still display normally as record chips
- Verify soft-deleted records still display as empty cells
