fix: restore green builds and align frontend-backend contracts (P0)

- Isolate Settings tests from .env and process env leakage
- Fix analytics metadata test to unwrap psycopg Json wrapper
- Remove unused state variables causing frontend build failures
- Fix ReviewPage to use /classifications endpoint instead of nonexistent /result
- Normalize ReviewPage status enums (failed not error) and access_type values
- Align api.ts types with backend response shapes (ReplayPage, AnalyticsData, AgentUsage)

frontend/src/pages/ReplayPage.tsx

@@ -1,4 +1,3 @@
-import { useState } from "react";
 import { useParams, useNavigate } from "react-router-dom";
 import { ReplayTimeline } from "../components/ReplayTimeline";
 
@@ -16,8 +15,6 @@ const MOCK_STEPS = [
 export function ReplayPage() {
   const { threadId } = useParams<{ threadId: string }>();
   const navigate = useNavigate();
-  const [page, setPage] = useState(1);
-
   if (!threadId) return null;
 
   return (