Make the app an installable PWA with phone layout and Web Push

Add a generated manifest, icon set, offline page and service worker that never caches authenticated HTML, plus install and update UI. Turn the rail into a drawer below md with container-query internals, dvh and safe-area handling, and reconnect the socket after visibility/network changes. Add Web Push subscriptions, presence-aware delivery, notification settings and tests.

src/functions/server/pwa/handle-pwa-file.ts

@@ -0,0 +1,53 @@
+import path from "path";
+import { PwaManifestPath, PwaServiceWorkerPath } from "@/src/data/pwa-data";
+
+const PUBLIC_DIR = path.resolve(import.meta.dir, "../../../../public");
+
+const PwaFiles: Record<string, string> = {
+    [PwaServiceWorkerPath]: "sw.js",
+    [PwaManifestPath]: "manifest.webmanifest",
+};
+
+/**
+ * Serves the service worker and the manifest with headers bunext's public
+ * handler can't give them: neither may be cached by a browser or a CDN,
+ * or a deploy waits an hour to reach installed apps. Only these two files
+ * are special; every other public asset keeps its normal caching.
+ */
+export default async function handlePwaFile({
+    pathname,
+}: {
+    pathname: string;
+}): Promise<Response | null> {
+    const file_name = PwaFiles[pathname];
+
+    if (!file_name) return null;
+
+    const file = Bun.file(path.join(PUBLIC_DIR, file_name));
+
+    if (!(await file.exists())) {
+        return new Response("Not Found", { status: 404 });
+    }
+
+    const headers = new Headers({
+        "Content-Type":
+            file_name.endsWith(".webmanifest")
+                ? "application/manifest+json; charset=utf-8"
+                : "text/javascript; charset=utf-8",
+        "Cache-Control": "no-store, max-age=0, must-revalidate",
+        "X-Content-Type-Options": "nosniff",
+    });
+
+    if (file_name == "sw.js") {
+        headers.set("Service-Worker-Allowed", "/");
+    }
+
+    const response = new Response(file, { headers });
+
+    /**
+     * `Bun.file` adds a filename disposition; a manifest is inline data.
+     */
+    response.headers.delete("content-disposition");
+
+    return response;
+}