## Why

The employee import narrows a duplicated "Vị trí" name by "Phòng ban" and "Công ty", but still rejects a row when the remaining positions cannot be told apart. This happens when two departments in the same company share a name, or when two companies share a name. The file has no other column to separate them, so the admin cannot import the row at all.

## What Changes

- Position resolution narrows step by step: "Vị trí" name → "Phòng ban" name → "Công ty" name.
- A row is rejected as `position_ambiguous` only when the remaining positions differ in a column the row left blank. The message names that column: "Phòng ban" first, then "Công ty".
- When the remaining positions have the same position, department and company names, the system takes the first one (lowest id) instead of rejecting the row.
- **BREAKING** (reason codes): `company_ambiguous` is removed. Companies with the same name are all kept in the company scope, and the rule above decides.

## Capabilities

### New Capabilities

### Modified Capabilities
- `employee-excel-import`: "Position Resolution in Employee Import" changes how it handles duplicates. Identical names fall back to the first position, ambiguity is reported per missing column, and `company_ambiguous` is removed.

## Impact

- **Code:** position and company resolution in `EmployeeController::import`.
- **API:** `errors[].reasons[].code` no longer returns `company_ambiguous`. The `position_ambiguous` message now names the missing column.
- **Tests:** `tests/Feature/EmployeeImportTest.php`.