chore: update MCP SDK from 1.27.1 to 1.28.0

- Pinned @modelcontextprotocol/sdk to 1.28.0 (was ^1.27.1)
- Updated CI dependency check to expect 1.28.0
- SDK 1.28.0 includes: loopback port relaxation, inputSchema fix,
  timeout cleanup fix, OAuth scope improvements
- All 15 MCP tool tests pass with no regressions

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

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

package.json

@@ -152,7 +152,7 @@
     "vitest": "^3.2.4"
   },
   "dependencies": {
-    "@modelcontextprotocol/sdk": "^1.27.1",
+    "@modelcontextprotocol/sdk": "1.28.0",
     "@n8n/n8n-nodes-langchain": "^2.13.1",
     "@supabase/supabase-js": "^2.57.4",
     "dotenv": "^16.5.0",