Remove the service worker (protect first loads)

Per Codex + Jay: the SW was added for nice-to-have PWA/offline caching, but it
sat in the boot path and put first loads at risk (post-deploy tiny-chunk stalls
of 4-10s — fast HTML, then delayed chunks). For a young site where a handful of
visitors a day IS the audience, a broken first impression is a huge share of
traffic. The site's value doesn't need offline caching; browser HTTP cache +
the Cloudflare edge are enough.

Removed cleanly (not just deleted — that strands the old worker on existing
clients):
- Delete src/service-worker.js → SvelteKit stops auto-registering.
- static/service-worker.js is now a one-shot KILL SWITCH: takes over, wipes all
  caches, unregisters itself, no fetch handler (requests go straight to network/
  browser cache). Served no-cache so existing clients pick it up.
- app.html boot script unregisters any worker + clears caches on load, as a
  backstop so no returning visitor stays stuck on the old boot path.

The boot seatbelt (timeout card, preloadError reload-once, telemetry) stays —
that, not the SW, was the real blank-screen protection. Build clean, 11 vitest.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/static/service-worker.js

@@ -0,0 +1,31 @@
+// Kill switch — the app no longer uses a service worker.
+//
+// It was added for nice-to-have PWA/offline caching, but it sat in the boot
+// path and put first loads at risk (post-deploy chunk stalls), which a young
+// site with few visitors can't afford. Browser HTTP cache + the Cloudflare edge
+// are enough for a news site.
+//
+// Existing visitors still have the OLD worker registered and controlling their
+// pages. This replacement (served at /service-worker.js, no-cache) takes over,
+// wipes the old caches, and unregisters itself. There is deliberately NO fetch
+// handler, so every request goes straight to the network / browser HTTP cache.
+// The app also unregisters any worker on load (see app.html) as a backstop.
+self.addEventListener('install', () => self.skipWaiting());
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    (async () => {
+      try {
+        const keys = await caches.keys();
+        await Promise.all(keys.map((k) => caches.delete(k)));
+      } catch (e) {
+        /* best effort */
+      }
+      try {
+        await self.registration.unregister();
+      } catch (e) {
+        /* best effort */
+      }
+    })()
+  );
+});