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/Pages/Admin/Settings.cshtml.cs

@@ -37,6 +37,10 @@ public class SettingsModel : PageModel
     [BindProperty] public string? SmsTemplate { get; set; }
     [BindProperty] public string? SmsSender { get; set; }
     [BindProperty] public string? NeshanMapKey { get; set; }
+    [BindProperty] public bool PushEnabled { get; set; }
+    [BindProperty] public string? VapidPublicKey { get; set; }
+    [BindProperty] public string? VapidPrivateKey { get; set; }
+    [BindProperty] public string? VapidSubject { get; set; }
     [TempData] public string? Saved { get; set; }
 
     public async Task OnGetAsync()
@@ -66,6 +70,10 @@ public class SettingsModel : PageModel
         SmsTemplate = s.SmsTemplate;
         SmsSender = s.SmsSender;
         NeshanMapKey = s.NeshanMapKey;
+        PushEnabled = s.PushEnabled;
+        VapidPublicKey = s.VapidPublicKey;
+        VapidPrivateKey = s.VapidPrivateKey;
+        VapidSubject = s.VapidSubject;
     }
 
     public async Task<IActionResult> OnPostAsync()
@@ -96,6 +104,10 @@ public class SettingsModel : PageModel
             SmsTemplate = SmsTemplate,
             SmsSender = SmsSender,
             NeshanMapKey = NeshanMapKey,
+            PushEnabled = PushEnabled,
+            VapidPublicKey = VapidPublicKey,
+            VapidPrivateKey = VapidPrivateKey,
+            VapidSubject = VapidSubject,
         });
         Saved = "تنظیمات ذخیره شد.";
         return RedirectToPage();