feat(grn): add update functionality for draft GRNs and support document-level discounts

- Implemented Update method in GrnsController to allow editing of draft GRNs.
- Enhanced CreateGrnRequest to include an optional totalDiscount property.
- Updated GrnService to handle GRN updates, including validation and line item processing.
- Modified NewGrnPage to support editing existing GRNs and applying document-level discounts.
- Improved UI in NewItemPage and GrnDetailPage for better user experience.
- Added search functionality to Select component for improved item selection.

Backend/ERPCore/Controllers/GrnsController.cs

@@ -42,6 +42,18 @@ public sealed class GrnsController : ApiControllerBase
         return Created($"/api/v1/grns/{dto.GrnId}", dto);
     }
 
+    /// <summary>Update a Draft GRN's header/lines.</summary>
+    [HttpPut("{grnId:int}")]
+    [ProducesResponseType(typeof(GrnDto), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    [ProducesResponseType(StatusCodes.Status422UnprocessableEntity)]
+    public async Task<ActionResult<GrnDto>> Update(int grnId, [FromBody] CreateGrnRequest request, CancellationToken ct)
+    {
+        var dto = await _grns.UpdateAsync(grnId, request, ct);
+        return Ok(dto);
+    }
+
     /// <summary>Confirm: create FIFO layers + inbound ledger + update PO receipts (single UoW txn).</summary>
     [HttpPost("{grnId:int}/confirm")]
     [ProducesResponseType(typeof(GrnConfirmResultDto), StatusCodes.Status200OK)]