Split App.jsx into pages + add service worker for offline support

App.jsx reduced from ~6,500 to ~3,900 lines by extracting each route into its
own page component (AdminPage, AuthPage, HomePage, ImportPage, ReaderPage,
SettingsPage, SetupPage, StudyPage). State and handlers are shared via
AppContext (React Context API); AppRouter handles routing at module level.

Also adds a network-first service worker (public/sw.js) that caches the last-
fetched Bible chapter data from bible.helloao.org and bolls.life so the app
stays usable when those APIs are temporarily unreachable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/sw.js

@@ -0,0 +1,36 @@
+const CACHE = 'bible-api-v1';
+const CACHEABLE = ['https://bible.helloao.org', 'https://bolls.life'];
+
+self.addEventListener('install', () => self.skipWaiting());
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys()
+      .then(keys => Promise.all(keys.filter(k => k !== CACHE).map(k => caches.delete(k))))
+      .then(() => self.clients.claim())
+  );
+});
+
+// Network-first, fall back to cache for external Bible API requests.
+self.addEventListener('fetch', (event) => {
+  if (!CACHEABLE.some(origin => event.request.url.startsWith(origin))) return;
+
+  event.respondWith(
+    fetch(event.request)
+      .then(response => {
+        if (response.ok) {
+          const clone = response.clone();
+          caches.open(CACHE).then(cache => cache.put(event.request, clone));
+        }
+        return response;
+      })
+      .catch(() =>
+        caches.open(CACHE)
+          .then(cache => cache.match(event.request))
+          .then(cached => cached ?? new Response('{"error":"offline"}', {
+            status: 503,
+            headers: { 'Content-Type': 'application/json' },
+          }))
+      )
+  );
+});