Inconsistent field-name uniqueness when adding fields.

Description
When creating a new project and adding a new field whose name starts with the same first two letters as an existing field, the UI shows the error "Field xx already exists. Won't be added to the project."
Despite the error, if the field is added during project creation it appears in the project — inconsistent behavior between add-via-create and add-later.

Environment
Staging

Application (+ app version, build, operating system)
iOS/Android

Steps to reproduce

1. Create a new project.
2. Try to add a new field named "Ab".
3. Try to add a new field named "Abc" (shares the same first two letters).
4. Observe the behavior when adding the field after project creation versus during project creation.

Actual results

1. When adding the field as part of creating a new project, UI shows: "Field xx already exists. Won't be added to the project." The field is added successfully despite the same-name-prefix, causing inconsistent behavior.

Expected results

1. Field uniqueness should be validated consistently. Either:
2. Uniqueness should be determined by the full field name (recommended).

Screen-record:

https://github.com/user-attachments/assets/5d613bd0-7bdf-4848-bd5e-ad93b9298b28

Reproduce the issue using the listed Ab/Abc sequence, then compare field-name validation during project creation with adding a field afterward. Done when full field names are validated consistently in both flows and the expected behavior is covered.