docs(csharp): note YAML authoring support in README

Removes the stale "YAML parsing — out of scope" entry now that the C# port
ships the YAML authoring front-end (ADR-0006). Adds the YamlDesugar / ParserYaml
files to the layout section and notes the YAML conformance runner alongside the
canonical-JSON one.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: dmealing

server/csharp/README.md

@@ -4,16 +4,16 @@ C# implementation of the MetaObjects metadata Loader. Targets .NET 8 (C# 12).
 
 ## What it covers
 
-- **Loader** — multi-file JSON loader with overlay merge and cross-file `extends:` resolution.
+- **Loader** — multi-file JSON / YAML loader with overlay merge and cross-file `extends:` resolution.
 - **Canonical serializer** — byte-identical output to the TypeScript reference (the cross-language wire format).
-- **Conformance runner** — auto-discovers `fixtures/conformance/*` and runs the shared corpus as `dotnet test`. The conformance corpus is the **oracle** — when a fixture goes red the port is wrong, never the fixture.
+- **YAML authoring front-end** — sigil-free attrs + `[]`-array suffix + fused-key default subtype + the D2 type-coercion guard (ADR-0006), via [YamlDotNet](https://github.com/aaubry/YamlDotNet). The cross-language interchange remains canonical JSON; YAML lowers to it.
+- **Conformance runners** — auto-discover `fixtures/conformance/*` AND `fixtures/yaml-conformance/*`, both shared with the other ports (TS/Python/Java). The conformance corpora are the **oracles** — when a fixture goes red the port is wrong, never the fixture.
 
 ## What it does NOT cover (out of scope)
 
 - Codegen (each language emits its own idiomatic per-language code; byte equivalence is not a goal at the codegen layer).
 - Runtime helpers (ObjectManager, filter parsing, CRUD endpoints) — per-language runtime concerns.
 - The `dbProvider` provider — the conformance corpus uses only `metaobjects-core-types`.
-- YAML parsing — the corpus is JSON only. A `MetaDataFormat.Yaml` enum value exists for source-discovery parity; the base loader throws on YAML content. The `ParseSource` seam is `protected virtual` so a future YAML port can drop in.
 
 ## Running
 
@@ -31,7 +31,9 @@ The test suite includes per-fixture `Lint` and `Conformance` theories over the s
   - `Meta/MetaData.cs` and the concrete node classes (`MetaRoot`, `MetaObject`, `MetaField`, etc.)
   - `CoreAttrSchemas.cs`, `CoreTypes.cs` — the `metaobjects-core-types` provider
   - `Parser.cs`, `SuperResolve.cs`, `SerializerJson.cs`
+  - `YamlDesugar.cs`, `ParserYaml.cs` — YAML authoring front-end (ADR-0006)
   - `Loader/` — `IMetaDataSource`, `InMemorySource`, `FileSource`, `MetaDataLoader`, `FileMetaDataLoader`, `ValidationPasses`
 - `MetaObjects.Conformance.Tests/` — xUnit test project + conformance harness
   - `ConformanceAdapter.cs`, `FixtureDiscovery.cs`, `OperationScript.cs`, `FixtureLint.cs`, `Navigator.cs`, `CapabilityBinding.cs`, `Result.cs`, `ExpectedFailures.cs`, `conformance-expected-failures.json`, `ConformanceTests.cs`
+  - `YamlConformanceTests.cs`, `YamlDesugarTests.cs`, `yaml-conformance-expected-failures.json` — YAML conformance + unit tests
   - Per-pipeline-stage unit tests (`ErrorsTests`, `RegistryTests`, `TreeTests`, `ParserTests`, `SerializerTests`, `LoaderTests`, `SuperResolveTests`, `ValidationTests`, …)