chore(showcase): mirror ms-agent-harness-dotnet wiring into sibling workflows

Three companion workflows duplicate the showcase_build.yml service registry
and were missed in the initial wiring commit. Bring them in sync:

- .github/workflows/showcase_build_check.yml: add ms_agent_harness_dotnet
  to the paths-filter and the ALL_SERVICES matrix (mirror of the
  production build matrix, used for pre-merge Docker build verification).
- .github/workflows/showcase_deploy.yml: add ms-agent-harness-dotnet to
  the workflow_dispatch options and the verification ALL_SERVICES with
  railway_id 6343d7f9-6c3f-4c8d-9a6e-79f03d2f1e37 and /api/health.
- .github/workflows/showcase_keep-alive.yml: add ms-agent-harness-dotnet
  to the keep-alive ping matrix.

Author: jpr5

.github/workflows/showcase_build_check.yml

@@ -73,6 +73,8 @@ jobs:
               - 'showcase/integrations/claude-sdk-typescript/**'
             ms_agent_dotnet:
               - 'showcase/integrations/ms-agent-dotnet/**'
+            ms_agent_harness_dotnet:
+              - 'showcase/integrations/ms-agent-harness-dotnet/**'
             claude_sdk_python:
               - 'showcase/integrations/claude-sdk-python/**'
             built_in_agent:
@@ -133,6 +135,7 @@ jobs:
             {"dispatch_name":"ms-agent-python","filter_key":"ms_agent_python","context":"showcase/integrations/ms-agent-python","image":"showcase-ms-agent-python","timeout":15,"lfs":false,"build_args":"","dockerfile":""},
             {"dispatch_name":"claude-sdk-typescript","filter_key":"claude_sdk_typescript","context":"showcase/integrations/claude-sdk-typescript","image":"showcase-claude-sdk-typescript","timeout":15,"lfs":false,"build_args":"","dockerfile":""},
             {"dispatch_name":"ms-agent-dotnet","filter_key":"ms_agent_dotnet","context":"showcase/integrations/ms-agent-dotnet","image":"showcase-ms-agent-dotnet","timeout":15,"lfs":false,"build_args":"","dockerfile":""},
+            {"dispatch_name":"ms-agent-harness-dotnet","filter_key":"ms_agent_harness_dotnet","context":"showcase/integrations/ms-agent-harness-dotnet","image":"showcase-ms-agent-harness-dotnet","timeout":15,"lfs":false,"build_args":"","dockerfile":""},
             {"dispatch_name":"claude-sdk-python","filter_key":"claude_sdk_python","context":"showcase/integrations/claude-sdk-python","image":"showcase-claude-sdk-python","timeout":15,"lfs":false,"build_args":"","dockerfile":""},
             {"dispatch_name":"built-in-agent","filter_key":"built_in_agent","context":"showcase/integrations/built-in-agent","image":"showcase-built-in-agent","timeout":15,"lfs":false,"build_args":"","dockerfile":""},
             {"dispatch_name":"shell-dojo","filter_key":"shell_dojo","context":".","image":"showcase-shell-dojo","timeout":10,"lfs":false,"build_args":"","dockerfile":"showcase/shell-dojo/Dockerfile"},

.github/workflows/showcase_deploy.yml

@@ -41,6 +41,7 @@ on:
           - ms-agent-python
           - claude-sdk-typescript
           - ms-agent-dotnet
+          - ms-agent-harness-dotnet
           - claude-sdk-python
           - built-in-agent
           - shell-dojo
@@ -110,6 +111,7 @@ jobs:
             {"dispatch_name":"ms-agent-python","railway_id":"655db75a-af8d-427d-a4f9-441570ae5003","health_path":"/api/health"},
             {"dispatch_name":"claude-sdk-typescript","railway_id":"18a98727-5700-44aa-b497-b60795dbbd6a","health_path":"/api/health"},
             {"dispatch_name":"ms-agent-dotnet","railway_id":"beeb2dd6-87a4-4599-aa07-0578f7bd6519","health_path":"/api/health"},
+            {"dispatch_name":"ms-agent-harness-dotnet","railway_id":"6343d7f9-6c3f-4c8d-9a6e-79f03d2f1e37","health_path":"/api/health"},
             {"dispatch_name":"claude-sdk-python","railway_id":"b122ab65-9854-4cb2-a68e-b50ff13f7481","health_path":"/api/health"},
             {"dispatch_name":"built-in-agent","railway_id":"f4f8371a-bc46-45b2-b6d4-9c9af608bdbf","health_path":"/api/health"},
             {"dispatch_name":"shell-dojo","railway_id":"7ad1ece7-2228-49cd-8a78-bddf30322907","health_path":"/"},

.github/workflows/showcase_keep-alive.yml

@@ -44,6 +44,7 @@ jobs:
           - llamaindex
           - mastra
           - ms-agent-dotnet
+          - ms-agent-harness-dotnet
           - ms-agent-python
           - pydantic-ai
           - spring-ai