feat(pwa): add service worker, manifest, and subpath-aware build

The precache list is generated from Bun.build's outputs, so hashed asset
names cannot drift. A waiting worker prompts to reload rather than
pinning the user to a stale build.

Two fixes beyond the brief: naming.entry changed from "[dir]/[name].[ext]"
to "[name].[ext]" because [dir] resolved to "src", putting index.html at
dist/src/index.html instead of the dist root; and external:
["*.webmanifest", "*.svg"] was added because Bun's HTML bundler otherwise
tries to resolve <link> hrefs as module imports, which fails outright for
the not-yet-generated manifest.webmanifest and would hash icon.svg,
breaking the fixed paths the manifest and service worker depend on.

happy-dom is registered per-file in src/ui/registerSw.test.ts only, not
as a global test preload, so src/domain/smoke.test.ts still guards the
domain layer's DOM-free invariant.

PNG icons (192px/512px) are not included — binary image generation isn't
available here; a human needs to add them for full Chrome installability.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/ui/App.tsx

@@ -7,6 +7,7 @@ import { PostMonthRoute } from "./routes/PostMonthRoute.tsx";
 import { PostYearRoute } from "./routes/PostYearRoute.tsx";
 import { SummaryRoute } from "./routes/SummaryRoute.tsx";
 import { SettingsRoute } from "./routes/SettingsRoute.tsx";
+import { UpdatePrompt } from "./components/UpdatePrompt.tsx";
 
 export function AppRoutes() {
   const year = currentMonth.slice(0, 4);
@@ -37,6 +38,7 @@ export function AppRoutes() {
           <Route path="*" element={<Navigate to={`/month/${currentMonth}`} replace />} />
         </Routes>
       </main>
+      <UpdatePrompt />
     </div>
   );
 }

src/ui/components/UpdatePrompt.tsx

@@ -0,0 +1,25 @@
+import { useEffect, useState } from "react";
+import { Button } from "@/components/ui/button";
+import { applyUpdate, registerServiceWorker } from "../registerSw.ts";
+
+export function UpdatePrompt() {
+  const [ready, setReady] = useState(false);
+
+  useEffect(() => {
+    registerServiceWorker(() => setReady(true));
+  }, []);
+
+  if (!ready) return null;
+
+  return (
+    <div className="fixed bottom-4 right-4 flex items-center gap-3 rounded border bg-background p-3 text-sm shadow-lg">
+      <span>A new version is ready.</span>
+      <Button size="sm" onClick={applyUpdate}>
+        Reload
+      </Button>
+      <Button size="sm" variant="ghost" onClick={() => setReady(false)}>
+        Later
+      </Button>
+    </div>
+  );
+}

src/ui/registerSw.test.ts

@@ -0,0 +1,12 @@
+import { GlobalRegistrator } from "@happy-dom/global-registrator";
+GlobalRegistrator.register();
+
+import { test, expect } from "bun:test";
+import { registerServiceWorker } from "./registerSw.ts";
+
+test("registration is a no-op when the browser has no service worker support", () => {
+  // happy-dom's navigator has no serviceWorker, which is the case under test.
+  // (happy-dom exposes `navigator` as a getter-only global, so there is
+  // nothing to save/restore here — reassigning it would throw.)
+  expect(() => registerServiceWorker(() => {})).not.toThrow();
+});

src/ui/registerSw.ts

@@ -0,0 +1,39 @@
+import { BASE_PATH, withBase } from "./basePath.ts";
+
+let waiting: ServiceWorker | null = null;
+
+/**
+ * Registers the worker and calls `onUpdateReady` when a new version is waiting.
+ * Without an explicit update path, a stale worker can pin the user to an old
+ * build indefinitely.
+ */
+export function registerServiceWorker(onUpdateReady: () => void): void {
+  if (typeof navigator === "undefined" || !("serviceWorker" in navigator)) return;
+
+  void navigator.serviceWorker
+    .register(withBase("sw.js"), { scope: BASE_PATH })
+    .then((registration) => {
+      if (registration.waiting) {
+        waiting = registration.waiting;
+        onUpdateReady();
+      }
+      registration.addEventListener("updatefound", () => {
+        const installing = registration.installing;
+        installing?.addEventListener("statechange", () => {
+          if (installing.state === "installed" && navigator.serviceWorker.controller) {
+            waiting = installing;
+            onUpdateReady();
+          }
+        });
+      });
+    })
+    .catch(() => {
+      // An unavailable worker must never break the app; it just means no offline.
+    });
+}
+
+export function applyUpdate(): void {
+  waiting?.postMessage({ type: "SKIP_WAITING" });
+  waiting = null;
+  window.location.reload();
+}