feat(server): share machines, post settings, clamps and nest defaults

Schema v13 adds shared_settings and shared_setting_revisions behind
/api/settings: one revision-guarded JSON document per kind and key, with
every revision (deletions included) kept with who saved it. Recreating a
deleted document continues its revision count.

OpenNest.Data gains the client (RemoteSharedSettings), a synchronous store
that keeps the last copy read for offline use and refuses writes while the
server is unreachable (SharedSettingsStore), a machine provider over it, and
JSON parse/serialize entry points for clamp settings and nest defaults.

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

OpenNest.Server.Tests/DrawingLibraryDatabaseTests.cs

@@ -22,7 +22,7 @@ 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(12L, Scalar(factory.DatabasePath, "PRAGMA user_version"));
+            Assert.Equal(13L, Scalar(factory.DatabasePath, "PRAGMA user_version"));
         }
 
         using var upgraded = new NestDatabase(factory.DatabasePath, pooling: false);
@@ -43,7 +43,7 @@ public sealed class DrawingLibraryDatabaseTests
 
         using (var database = new NestDatabase(factory.DatabasePath, pooling: false))
         {
-            Assert.Equal(12L, Scalar(factory.DatabasePath, "PRAGMA user_version"));
+            Assert.Equal(13L, 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.
@@ -80,7 +80,7 @@ public sealed class DrawingLibraryDatabaseTests
     {
         using var factory = new ServerFactory();
         using (new NestDatabase(factory.DatabasePath, pooling: false)) { }
-        Execute(factory.DatabasePath, "PRAGMA user_version=13");
+        Execute(factory.DatabasePath, "PRAGMA user_version=14");
 
         Assert.Throws<InvalidOperationException>(() => new NestDatabase(factory.DatabasePath, pooling: false));
     }