Cut RethinkDB

Remove the vendored RethinkDb driver and its Linq provider, the Rethink
backing store, the already-stubbed RethinkConnection, the Rethink test
window, and the Rethink-only Remotion.Linq and Logging.Abstractions DLLs.
The database editor now works only on GameData/AetherDB.msgpack, with a
Save button replacing the dead Connect UI and broken JSON export.
RethinkTable becomes DatabaseCategory, which only groups editor entries.

Economy.Server still references Rethink; it was already unbuildable and
is handled separately.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Assets/Scripts/ServerShared/CultCache/Serialization/RegisterResolver.cs

@@ -4,7 +4,6 @@ using MessagePack;
 using MessagePack.ReactivePropertyExtension;
 using MessagePack.Resolvers;
 using Newtonsoft.Json;
-using RethinkDb.Driver.Net;
 
 public static class RegisterResolver
 {
@@ -29,11 +28,7 @@ public static class RegisterResolver
         {
             Converters = new List<JsonConverter>
             {
-                new MathJsonConverter(),
-                Converter.DateTimeConverter,
-                Converter.BinaryConverter,
-                Converter.GroupingConverter,
-                Converter.PocoExprConverter
+                new MathJsonConverter()
             }
         };