fix(buf): generate C# service clients from aggregate template

AGENTS.md

@@ -112,7 +112,10 @@ Shared type modules: `common.proto`, `spatial_types.proto`,
 
 Generation flow: `buf.gen.yaml` (v2) drives multi-language output to `gen/`
 with managed-mode package prefixes (`github.com/geospatial-grpc/proto-go`,
-`io.grpc.geospatial`, C# base namespace `GeospatialGrpc`). The .NET package
+`io.grpc.geospatial`). C# uses no `base_namespace` override: managed mode
+derives the namespace from the proto package (`geospatial.v1` -> `Geospatial.V1`),
+and a `base_namespace` that is not a prefix of that namespace makes the C#
+plugin hard-fail (so `GeospatialGrpc` must not be set). The .NET package
 instead compiles the protos directly via `Grpc.Tools` (`GrpcServices=Both`).
 
 ## Directory Layout

buf.gen.yaml

@@ -15,6 +15,8 @@ plugins:
   # published NuGet package.
   - remote: buf.build/protocolbuffers/csharp:v35.1
     out: gen/csharp
+  - remote: buf.build/grpc/csharp:v1.81.1
+    out: gen/csharp
 
   # Go
   - remote: buf.build/protocolbuffers/go:v1.36.11