Posthog-fixes (#5901)

PostHog is now initialized with persistence: 'memory' so no cookies are
written on first load. Consent is handled in a PostHogConsentSync
component that switches to localStorage+cookie persistence only when the
user accepts, using the official @posthog/react package (cherry-picked
from 14aaf64)

---------

Co-authored-by: James Brunton <[email protected]>

frontend/tsconfig.proprietary.json

@@ -11,9 +11,6 @@
       ],
       "@proprietary/*": [
         "src/proprietary/*"
-      ],
-      "posthog-js/react": [
-        "node_modules/posthog-js/react/dist/types/index.d.ts"
       ]
     }
   },
@@ -25,4 +22,4 @@
     "src/core/setupTests.ts",
     "src/proprietary"
   ]
-}
+}