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/backend/db/push/is-user-present.ts

@@ -0,0 +1,24 @@
+import BunSQLite from "@moduletrace/bun-sqlite";
+import type { BUN_SQLITE_COBBLE_USER_PRESENCE } from "@/db/types/db";
+import { AppData } from "@/src/data/app-data";
+
+/**
+ * Whether the app is open for this user right now (any process), based on
+ * the socket keepalive. Push notifications are skipped while it is.
+ */
+export default async function isUserPresent({
+    user_id,
+}: {
+    user_id: number | string;
+}) {
+    const row = (
+        await BunSQLite.sql<BUN_SQLITE_COBBLE_USER_PRESENCE>({
+            sql: `SELECT last_seen_at FROM user_presence WHERE user_id = ? LIMIT 1`,
+            values: [user_id],
+        })
+    ).payload?.[0];
+
+    if (!row?.last_seen_at) return false;
+
+    return Date.now() - Number(row.last_seen_at) <= AppData.PushPresenceWindowMs;
+}