PWA: installable app (web/win/android/ios) + download/help page + push notifications

- manifest.webmanifest + service worker (offline shell + push + notificationclick) + PNG icons (192/512/apple) + iOS meta + SW registration → installable everywhere
- /Download page: per-OS install help (web/windows/android/ios), install button (beforeinstallprompt), 'enable notifications' flow, usage guide, Bazaar/TWA note; nav + footer links
- Web Push foundation: WebPushSubscription entity + /push/subscribe (stores), VAPID + push settings in /Admin/Settings, on-device local notification; server broadcast documented (WebPush via Nexus)
- docs/PWA-TWA.md: VAPID keygen, server-push wiring, Bubblewrap→Cafe Bazaar + assetlinks steps
- Verified: manifest/sw/icons served, download page, subscribe stores (200), layout wired

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

src/JobsMedical.Web/Models/AppSetting.cs

@@ -66,6 +66,12 @@ public class AppSetting
     /// (Google Maps is blocked in Iran). Empty → only the "my location" button is shown.</summary>
     [MaxLength(200)] public string? NeshanMapKey { get; set; }
 
+    // --- Web Push (PWA notifications). VAPID keypair; generate once with the web-push tooling. ---
+    public bool PushEnabled { get; set; } = false;
+    [MaxLength(200)] public string? VapidPublicKey { get; set; }
+    [MaxLength(200)] public string? VapidPrivateKey { get; set; }
+    [MaxLength(120)] public string? VapidSubject { get; set; } = "mailto:admin@hamkadr.ir";
+
     public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
 
     /// <summary>Split a textarea (newline/comma separated) into trimmed non-empty items.</summary>