Phase 2: API client, typed hooks, live probe

- Add api:types script (openapi-typescript against live FastAPI)
- Generate src/lib/api/types.ts (2972 lines, 55 paths, 16 schemas)
- lib/api/client.ts: typed apiRequest + ApiError + makeQueryClient
  (staleTime 5s, no refetchOnWindowFocus to preserve editor state)
- lib/providers.tsx: QueryClientProvider client component, useState
  singleton so App Router re-renders don't dump the cache
- lib/api/cases.ts: Case type + casesKeys + useCases hook (pragmatic
  hand-typed Case pending backend response-model annotations)
- layout.tsx: wrap children with <Providers>
- Smoke test: CasesLiveProbe component on home page hitting live FastAPI
  via /api/cases rewrite proxy

Phase 2 deliverable check: useCases() returns typed Case[] from the
production FastAPI through the Next.js proxy. End-to-end wiring proven.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web-ui/src/lib/api/client.ts

@@ -0,0 +1,77 @@
+/**
+ * API client — typed fetch wrapper + TanStack Query setup.
+ *
+ * All requests hit relative URLs (e.g. `/api/cases`) which next.config.ts
+ * rewrites transparently proxy to legal-ai.nautilus.marcusgroup.org. No CORS
+ * gymnastics, no direct public-URL references in component code.
+ */
+
+import { QueryClient } from "@tanstack/react-query";
+
+export class ApiError extends Error {
+  constructor(
+    message: string,
+    public readonly status: number,
+    public readonly body: unknown,
+  ) {
+    super(message);
+    this.name = "ApiError";
+  }
+}
+
+type RequestOptions = {
+  method?: "GET" | "POST" | "PUT" | "PATCH" | "DELETE";
+  body?: unknown;
+  signal?: AbortSignal;
+};
+
+/**
+ * Typed JSON request. Throws ApiError on non-2xx responses with the parsed body.
+ * Always returns parsed JSON — callers pass the expected type parameter.
+ */
+export async function apiRequest<T>(
+  path: string,
+  { method = "GET", body, signal }: RequestOptions = {},
+): Promise<T> {
+  const res = await fetch(path, {
+    method,
+    headers: body ? { "Content-Type": "application/json" } : undefined,
+    body: body ? JSON.stringify(body) : undefined,
+    signal,
+  });
+
+  const contentType = res.headers.get("content-type") ?? "";
+  const parsed = contentType.includes("application/json")
+    ? await res.json().catch(() => null)
+    : await res.text().catch(() => null);
+
+  if (!res.ok) {
+    throw new ApiError(
+      `${method} ${path} failed with ${res.status}`,
+      res.status,
+      parsed,
+    );
+  }
+
+  return parsed as T;
+}
+
+/**
+ * Shared TanStack Query client. Defaults are tuned for a dashboard that polls
+ * for case progress — stale for 5 seconds, 1 automatic retry, no background
+ * refetch on window focus (preserves editor state during long sessions).
+ */
+export function makeQueryClient(): QueryClient {
+  return new QueryClient({
+    defaultOptions: {
+      queries: {
+        staleTime: 5_000,
+        retry: 1,
+        refetchOnWindowFocus: false,
+      },
+      mutations: {
+        retry: 0,
+      },
+    },
+  });
+}