feat(nesting): nest higher priority numbers first

Priority worked like a rank (lower first) with a default of 0, and the
Edit Drawing form stopped at 0, so moving one part ahead of the rest
meant renumbering every other drawing. Higher-first lets a user raise a
single part to 1 and leave everything else at the default.

Every engine, filler and candidate comparer now serves the highest tier
first. Stored values keep their order:
- .nest files add `nestPriority` and keep writing the negated value under
  `priority`, so older readers nest in the same order; files without
  `nestPriority` are negated on read. Drawing packages strip both, so
  package hashes are unchanged.
- Library settings send both keys the same way for older clients.
- Server schema v18 negates stored drawing priorities (an older server
  refuses the upgraded database).
- Job documents move to version 2; version 1 jobs are converted, and an
  older worker refuses version 2 instead of reversing the order.

The Edit Drawing form now accepts negative priorities and says higher
numbers nest first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Server.Tests/DrawingLibraryDatabaseTests.cs

@@ -23,7 +23,7 @@ public sealed class DrawingLibraryDatabaseTests
             using (var database = new NestDatabase(factory.DatabasePath, pooling: false))
                 Assert.Empty(database.QueryDrawings(new DrawingLibraryQuery { IncludeArchived = true }).Items);
             Assert.Equal(before, NestDigest(factory.DatabasePath));
-            Assert.Equal(17L, Scalar(factory.DatabasePath, "PRAGMA user_version"));
+            Assert.Equal(18L, Scalar(factory.DatabasePath, "PRAGMA user_version"));
         }
 
         using var upgraded = new NestDatabase(factory.DatabasePath, pooling: false);
@@ -44,7 +44,7 @@ public sealed class DrawingLibraryDatabaseTests
 
         using (var database = new NestDatabase(factory.DatabasePath, pooling: false))
         {
-            Assert.Equal(17L, Scalar(factory.DatabasePath, "PRAGMA user_version"));
+            Assert.Equal(18L, Scalar(factory.DatabasePath, "PRAGMA user_version"));
             Assert.Equal(before, NestDigest(factory.DatabasePath));
             // Two distinct blobs across four revisions: the bracket's notes edit and the
             // plate both reuse the bracket's first package.
@@ -81,11 +81,37 @@ public sealed class DrawingLibraryDatabaseTests
     {
         using var factory = new ServerFactory();
         using (new NestDatabase(factory.DatabasePath, pooling: false)) { }
-        Execute(factory.DatabasePath, "PRAGMA user_version=18");
+        Execute(factory.DatabasePath, "PRAGMA user_version=19");
 
         Assert.Throws<InvalidOperationException>(() => new NestDatabase(factory.DatabasePath, pooling: false));
     }
 
+    [Fact]
+    public void V18Upgrade_NegatesLowerFirstPrioritiesInEveryRevision()
+    {
+        using var factory = new ServerFactory();
+        var record = Record();
+        var other = Record("Synthetic plate");
+        using (var database = new NestDatabase(factory.DatabasePath, pooling: false))
+        {
+            database.InsertDrawing(record.Id, record, Package());
+            database.InsertDrawing(other.Id, other, Package("other"));
+        }
+        // A v17 library stored lower-first values: 3 nested before 0, and int.MinValue before both.
+        Execute(factory.DatabasePath, $"""
+            UPDATE drawings SET priority = 3 WHERE id = '{record.Id}';
+            UPDATE drawing_revisions SET priority = 3 WHERE id = '{record.Id}';
+            UPDATE drawings SET priority = -2147483648 WHERE id = '{other.Id}';
+            PRAGMA user_version=17;
+            """);
+
+        using var upgraded = new NestDatabase(factory.DatabasePath, pooling: false);
+        Assert.Equal(18L, Scalar(factory.DatabasePath, "PRAGMA user_version"));
+        Assert.Equal(-3, upgraded.GetDrawing(record.Id)!.Settings.Priority);
+        Assert.Equal(-3, Assert.Single(upgraded.DrawingHistory(record.Id, 0, 100)!.Items).Settings.Priority);
+        Assert.Equal(int.MaxValue, upgraded.GetDrawing(other.Id)!.Settings.Priority);
+    }
+
     [Fact]
     public void FailedDrawingMigration_RollsBackAndCanRestart()
     {