Decouple MCP NuGet publish from GitHub Release events

The MCP package versions independently from core Testimize, so reacting
to release:published (which carries the core v* tag) would publish MCP
at the wrong version. Trigger only on mcp-v* tags or manual dispatch.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: angelovstanton

.github/workflows/publish-mcp-nuget.yml

@@ -4,8 +4,6 @@ on:
   push:
     tags:
       - 'mcp-v*.*.*'  # Triggers on MCP version tags like mcp-v1.0.0
-  release:
-    types: [published]
   workflow_dispatch:
     inputs:
       version: