docs: send docs pageviews to the HyperFrames PostHog project (#5948)

The landing page and hyperframes.dev are tracked; the docs are not, so
AI-chat referrals and docs-to-download paths are invisible. Session
recording stays off.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

docs/docs.json

@@ -1286,5 +1286,11 @@
       "destination": "/sdk/quickstart",
       "permanent": true
     }
-  ]
+  ],
+  "integrations": {
+    "posthog": {
+      "apiKey": "phc_zjjbX0PnWxERXrMHhkEJWj9A9BhGVLRReICgsfTMmpx",
+      "sessionRecording": false
+    }
+  }
 }