Add ApiClient React context provider with useApiClient hook

src/shared/api/provider.tsx

@@ -0,0 +1,41 @@
+import { createContext, useContext } from "react";
+import type { ReactNode } from "react";
+import type { ApiClient } from "./client.js";
+
+const ApiClientContext = createContext<ApiClient | null>(null);
+
+export interface ApiClientProviderProps {
+  client: ApiClient;
+  children: ReactNode;
+}
+
+/**
+ * Provides the ApiClient instance to the React tree. SSR-aware:
+ * on the server, construct per-request with the resolved locale;
+ * on the client, share a single instance across the tab.
+ */
+export function ApiClientProvider({
+  client,
+  children,
+}: ApiClientProviderProps): JSX.Element {
+  return (
+    <ApiClientContext.Provider value={client}>
+      {children}
+    </ApiClientContext.Provider>
+  );
+}
+
+/**
+ * Returns the ApiClient from context. Throws if used outside
+ * <ApiClientProvider>.
+ */
+export function useApiClient(): ApiClient {
+  const client = useContext(ApiClientContext);
+  if (!client) {
+    throw new Error(
+      "useApiClient() must be used within an <ApiClientProvider>. " +
+      "Ensure the root layout wraps the tree with <ApiClientProvider>.",
+    );
+  }
+  return client;
+}