Move PWA registration into useEffect to avoid render-phase side effects

registerSW() and setUpdateSW() were being called during component render,
which triggers a state update during rendering and can cause infinite
re-render loops. This also caused the Playwright E2E tests to fail since
they block service workers and the render-phase side effect destabilizes
React hydration.

Move both calls into a useEffect that runs once on mount, gated on
import.meta.env.PROD.

ui/src/client.tsx

@@ -1,5 +1,5 @@
 import { StartClient } from "@tanstack/react-start/client"
-import { StrictMode, useState } from "react"
+import { StrictMode, useEffect, useState } from "react"
 import { hydrateRoot } from "react-dom/client"
 import { registerSW } from "virtual:pwa-register"
 
@@ -15,14 +15,15 @@ function PwaUpdateProvider() {
   const [needRefresh, setNeedRefresh] = useState(false)
   const [updateSW, setUpdateSW] = useState<(() => Promise<void>) | undefined>(undefined)
 
-  if (import.meta.env.PROD) {
+  useEffect(() => {
+    if (!import.meta.env.PROD) return
     const updateSWRef = registerSW({
       onNeedRefresh() {
         setNeedRefresh(true)
       },
     })
     setUpdateSW(() => updateSWRef)
-  }
+  }, [])
 
   return (
     <PwaUpdateToast