fix(drive-integration): treat Add Entry references as child of existing parent [INTEG-4524]

[JuliRossi]

INTEG-4524

Summary

• Collapse Add Entry into a single-screen form (AddEntryForm) with conditional reference controls.
• Flip reference semantics: the new entry is a child of an existing parent (not a parent pointing at an existing entry).
• On Yes: pick parent entry → pick parent reference field when the parent has more than one → write __ref / sourceEntryIds on the parent and edge from=parent → to=child.
• Single Link fields replace any prior child; Array fields append.
• Disable Yes only when no existing parent content type has an Entry reference field.

New reference logic

flowchart TD
  A[Select content type for new entry] --> B{Any existing parent<br/>has Entry reference fields?}
  B -->|No| C[Yes disabled — only No allowed]
  B -->|Yes| D{Should this new entry be a<br/>reference of an existing entry?}
  D -->|No| E[Map fields on new entry only]
  D -->|Yes| F[Select parent entry]
  F --> G{Parent has how many<br/>Entry reference fields?}
  G -->|0| H[Save disabled]
  G -->|1| I[Auto-pick that field]
  G -->|2+| J[Select parent field]
  I --> K[Save]
  J --> K
  K --> L[Create new child entry]
  L --> M{Parent field type}
  M -->|Link| N[Replace parent field value,<br/>sourceEntryIds, and edges]
  M -->|Array| O[Append child to parent field,<br/>sourceEntryIds, and edges]
  N --> P["Edge: from=parent → to=child"]
  O --> P

Loading

Before vs after

	Before (wrong)	After
Who holds __ref	New entry	Parent entry
Reference fields shown	New content type	Parent content type
Graph edge	from=new → to=existing	from=parent → to=child
Yes disabled when	New CT has no ref fields	No parent can accept a ref

Test plan

• Add entry No → saves standalone entry with mapped fields
• Add entry Yes with parent that has one Link field → links as child without showing field select
• Add entry Yes with parent that has multiple ref fields → field select appears; Save requires a choice
• Parent already has a filled single Link → creating a new child replaces the old reference on create (old id gone from sourceEntryIds / payload)
• Parent Array reference → new child is appended
• When every existing entry’s CT has no Entry refs → Yes is disabled, No still works
• New entry CT with no ref fields (e.g. Component/Tag) but parents can accept refs → Yes stays enabled

[JuliRossi]

Dividing this into 2 PRs, so it is easier to review