chore(repo): remove polygraph plugin entry from claude settings (#35370)

## Current Behavior

`.claude/settings.json` enables `polygraph@nx-claude-plugins`, but the
`nx-claude-plugins` marketplace only ships the `nx` plugin. The
`polygraph` plugin lives in the separate `polygraph-plugins`
marketplace, which is not declared in `extraKnownMarketplaces` either —
so the entry refers to a plugin+marketplace pair that doesn't exist.
Every contributor picks up the broken id when they pull the repo.

The bad id was introduced in #34790, which moved to the new plugin but
left the marketplace name pointing at the old one.

## Expected Behavior

Polygraph is now installed globally via the session-start opt-in prompt,
so the repo-level `enabledPlugins` entry is no longer needed. Remove it
entirely rather than pointing it at a marketplace the settings file
doesn't declare.

Author: leosvelperez

.claude/settings.json

@@ -41,7 +41,6 @@
     }
   },
   "enabledPlugins": {
-    "nx@nx-claude-plugins": true,
-    "polygraph@nx-claude-plugins": true
+    "nx@nx-claude-plugins": true
   }
 }