feat(api): accept complete nesting jobs and report fulfillment

Task 6 of the whole-job engine API: adapt the public NestRequest/NestRunner/
NestResponse surface to delegate to the whole-job runner instead of a manual
quantity loop.

- NestRequest: optional explicit Plates stock list (null keeps the legacy
  unlimited SheetSize fallback; empty list means no available stock),
  optional per-part Id (derived as part-{index} when absent), and an explicit
  PlacementStrategy that takes precedence over the legacy Strategy.
- NestRequestPlate: one physical-stock type (id, size, quantity, spacing,
  quadrant).
- NestRunner: imports each DXF once, propagates priority/rotation constraints,
  runs a single NestJobRunner solve, materializes ID/pose placements exactly
  once, and reports aggregate utilization as total placed part area over total
  physical sheet area.
- NestResponse: exposes status, stop reason, part fulfillment, stock usage,
  and plate-to-stock mapping; .nestquote save/load gains a schema version and
  reports completion as unknown for old archives lacking fulfillment metadata.
- Tests: extend the Api request/runner/persistence suites for legacy SheetSize,
  explicit mixed finite stock, stock exhaustion, weighted utilization, old
  archive loading, and new-archive round trips.

Verification: cross-compiles clean on net8.0-windows (Linux). The Api tests
require a Windows runner (net8.0-windows) and are NOT executed here; the
delegated engine logic is covered by the 70-test net8.0 Engine.Tests suite
(committed in Task 5). Windows runtime verification remains outstanding.

OpenNest.Tests/Api/NestRequestTests.cs

@@ -13,6 +13,8 @@ public class NestRequestTests
         Assert.Empty(request.Parts);
         Assert.Equal(60, request.SheetSize.Width);
         Assert.Equal(120, request.SheetSize.Length);
+        Assert.Null(request.Plates);
+        Assert.Equal("Default", request.PlacementStrategy);
         Assert.Equal("Steel, A1011 HR", request.Material);
         Assert.Equal(0.06, request.Thickness);
         Assert.Equal(0.1, request.Spacing);
@@ -38,8 +40,38 @@ public class NestRequestTests
     {
         var part = new NestRequestPart { DxfPath = "part.dxf" };
 
+        Assert.Null(part.Id);
         Assert.Equal(1, part.Quantity);
         Assert.True(part.AllowRotation);
         Assert.Equal(0, part.Priority);
     }
+
+    [Fact]
+    public void ExplicitPlates_PreserveStockSettings()
+    {
+        var request = new NestRequest
+        {
+            Plates =
+            [
+                new NestRequestPlate
+                {
+                    Id = "remnant",
+                    Size = new Size(24, 48),
+                    Quantity = 3,
+                    PartSpacing = 0.2,
+                    EdgeSpacing = new Spacing(1, 2, 3, 4),
+                    Quadrant = 3
+                }
+            ]
+        };
+
+        var plate = Assert.Single(request.Plates!);
+        Assert.Equal("remnant", plate.Id);
+        Assert.Equal(24, plate.Size.Width);
+        Assert.Equal(48, plate.Size.Length);
+        Assert.Equal(3, plate.Quantity);
+        Assert.Equal(0.2, plate.PartSpacing);
+        Assert.Equal(new Spacing(1, 2, 3, 4), plate.EdgeSpacing);
+        Assert.Equal(3, plate.Quadrant);
+    }
 }