fix(web): append /api to baseUrl for shared clients

getBaseUrl() returns 'http://localhost:4003' without /api suffix.
Shared feature-flag-client and subscription-client expect the API
prefix in the URL. Without this fix, requests hit /flags/poll and
/subscriptions/me instead of /api/flags/poll and /api/subscriptions/me.

web/src/lib/billing-client.ts

@@ -17,7 +17,7 @@ let _client: ReturnType<typeof createSubscriptionClient> | null = null;
 function getClient() {
   if (!_client) {
     _client = createSubscriptionClient({
-      baseUrl: getBaseUrl(),
+      baseUrl: `${getBaseUrl()}/api`,
       productId: PRODUCT_ID,
       userId: 'me',
       getAccessToken: () => getAuthClient().getAccessToken() ?? '',