chore: remove standalone mcp/ package and CI triggers

The MCP server is now a built-in endpoint on the Worker. Remove the
mcp/ directory, its trigger paths in release-packages.yml, and the
mcp entry in detect-releases.sh.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: DennisAlund

.github/workflows/release-packages.yml

@@ -5,7 +5,6 @@ on:
     branches: [main]
     paths:
       - sdk/package.json
-      - mcp/package.json
 
 permissions:
   contents: write