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/Migrations/AppDbContextModelSnapshot.cs

@@ -93,6 +93,9 @@ namespace JobsMedical.Web.Migrations
                         .HasMaxLength(200)
                         .HasColumnType("character varying(200)");
 
+                    b.Property<bool>("PushEnabled")
+                        .HasColumnType("boolean");
+
                     b.Property<string>("SmsApiKey")
                         .HasMaxLength(200)
                         .HasColumnType("character varying(200)");
@@ -118,6 +121,18 @@ namespace JobsMedical.Web.Migrations
                     b.Property<DateTime>("UpdatedAt")
                         .HasColumnType("timestamp with time zone");
 
+                    b.Property<string>("VapidPrivateKey")
+                        .HasMaxLength(200)
+                        .HasColumnType("character varying(200)");
+
+                    b.Property<string>("VapidPublicKey")
+                        .HasMaxLength(200)
+                        .HasColumnType("character varying(200)");
+
+                    b.Property<string>("VapidSubject")
+                        .HasMaxLength(120)
+                        .HasColumnType("character varying(120)");
+
                     b.HasKey("Id");
 
                     b.ToTable("AppSettings");
@@ -668,6 +683,44 @@ namespace JobsMedical.Web.Migrations
                     b.ToTable("Visitors");
                 });
 
+            modelBuilder.Entity("JobsMedical.Web.Models.WebPushSubscription", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("Auth")
+                        .IsRequired()
+                        .HasMaxLength(100)
+                        .HasColumnType("character varying(100)");
+
+                    b.Property<DateTime>("CreatedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<string>("Endpoint")
+                        .IsRequired()
+                        .HasMaxLength(600)
+                        .HasColumnType("character varying(600)");
+
+                    b.Property<string>("P256dh")
+                        .IsRequired()
+                        .HasMaxLength(200)
+                        .HasColumnType("character varying(200)");
+
+                    b.Property<string>("VisitorId")
+                        .HasMaxLength(36)
+                        .HasColumnType("character varying(36)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("Endpoint")
+                        .IsUnique();
+
+                    b.ToTable("WebPushSubscriptions");
+                });
+
             modelBuilder.Entity("JobsMedical.Web.Models.Application", b =>
                 {
                     b.HasOne("JobsMedical.Web.Models.User", "Doctor")