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/src/app.html

@@ -38,6 +38,19 @@
       // screen. Show a calm recovery card if the app hasn't mounted, and reload
       // once on a chunk/preload failure (e.g. a just-deployed hashed chunk).
       (function () {
+        // The service worker was removed (it risked first loads). Actively
+        // unregister any worker a returning visitor still has + wipe its caches,
+        // so nobody stays stuck on the old boot path. Runs on every load; cheap.
+        if ('serviceWorker' in navigator) {
+          try {
+            navigator.serviceWorker.getRegistrations()
+              .then(function (rs) { rs.forEach(function (r) { r.unregister(); }); })
+              .catch(function () {});
+            if (self.caches && caches.keys) {
+              caches.keys().then(function (ks) { ks.forEach(function (k) { caches.delete(k); }); }).catch(function () {});
+            }
+          } catch (e) { /* best effort */ }
+        }
         var sent = false;
         function report(reason) {
           if (sent) return; sent = true;             // one beacon per page