fix(.mcp.json): wrap playwright under mcpServers key

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.mcp.json

@@ -1,4 +1,5 @@
 {
+  "mcpServers": {
     "playwright": {
       "command": "npx",
       "args": [
@@ -8,4 +9,5 @@
         "_diag"
       ]
     }
+  }
 }