feat(examples)+test(e2e): counter service worker; bankai dev+prod in Chromium

The counter example gains a sw.js exercising bankai's injected-precache
build. e2e proves both bankai paths in real Chromium: the built app
serves, hydrates and runs with zero console errors and zero mismatch
warnings (and choo consumed window.initialState), and the dev server's
Vite-transformed virtual entry hydrates the same way.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014NgfSjHE11oFpoSnLVKLXd

examples/counter/sw.js

@@ -0,0 +1,28 @@
+/* global __BANKAI_ASSETS__ */
+// Service worker built by `bankai build`: the precache list is injected
+// at build time from the asset manifest (the choo-service-worker
+// convention, manifest edition). Register it from your app with
+// navigator.serviceWorker.register('/sw.js').
+
+const CACHE = 'counter-v1'
+const ASSETS = __BANKAI_ASSETS__
+
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE).then((cache) => cache.addAll(ASSETS))
+  )
+})
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((keys) =>
+      Promise.all(keys.filter((k) => k !== CACHE).map((k) => caches.delete(k)))
+    )
+  )
+})
+
+self.addEventListener('fetch', (event) => {
+  event.respondWith(
+    caches.match(event.request).then((hit) => hit || fetch(event.request))
+  )
+})