Build against plugin API 0.1.19-mm.1; item header words from the host

The contract now reports each object's description header, so the item
record carries the words the original's framework filed from it: the weenie
and second header flags, the physics description flags, the setup id, the
scale key (0.0 whenever a scale was sent, as recorded), the hook type, the
parent and parent location, and the framework's own summary word (key
218103831: stackable, has a position, lockable, inscribable, usable,
container), derived from the header by a rule that matches all 2,220 recorded
items carrying both words. With the header flags known, key presence follows
the header exactly instead of guessing from non-zero values: a recorded
Pyreal Mote now rebuilds key for key.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Directory.Build.props

@@ -15,7 +15,7 @@
     <!-- The plugin contract, compile-only, from the .nupkg in ./packages-local
          (downloaded from the OpenAC release of the same version). The host
          supplies the contract assembly at runtime. -->
-    <PluginApiPackageVersion>0.1.19-mmpreview.1</PluginApiPackageVersion>
+    <PluginApiPackageVersion>0.1.19-mm.1</PluginApiPackageVersion>
     <RestorePackagesWithLockFile>false</RestorePackagesWithLockFile>
   </PropertyGroup>
 </Project>