[Infra] Persist DataProtection keys in the DB (fixes logout/antiforgery on deploy)

Add Microsoft.AspNetCore.DataProtection.EntityFrameworkCore; AppDbContext implements IDataProtectionKeyContext with a DataProtectionKeys set; PersistKeysToDbContext + SetApplicationName(hamkadr). Now the key ring is shared across restarts/replicas, so auth cookies, antiforgery tokens and the captcha no longer break on every deploy (the root cause of the earlier admin lock-out). Migration: DataProtectionKeys table.

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

src/JobsMedical.Web/Migrations/20260607040208_DataProtectionKeys.cs

@@ -0,0 +1,36 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+
+#nullable disable
+
+namespace JobsMedical.Web.Migrations
+{
+    /// <inheritdoc />
+    public partial class DataProtectionKeys : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "DataProtectionKeys",
+                columns: table => new
+                {
+                    Id = table.Column<int>(type: "integer", nullable: false)
+                        .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.IdentityByDefaultColumn),
+                    FriendlyName = table.Column<string>(type: "text", nullable: true),
+                    Xml = table.Column<string>(type: "text", nullable: true)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_DataProtectionKeys", x => x.Id);
+                });
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "DataProtectionKeys");
+        }
+    }
+}

src/JobsMedical.Web/Migrations/AppDbContextModelSnapshot.cs

@@ -970,6 +970,25 @@ namespace JobsMedical.Web.Migrations
                     b.ToTable("WebPushSubscriptions");
                 });
 
+            modelBuilder.Entity("Microsoft.AspNetCore.DataProtection.EntityFrameworkCore.DataProtectionKey", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("FriendlyName")
+                        .HasColumnType("text");
+
+                    b.Property<string>("Xml")
+                        .HasColumnType("text");
+
+                    b.HasKey("Id");
+
+                    b.ToTable("DataProtectionKeys");
+                });
+
             modelBuilder.Entity("JobsMedical.Web.Models.Application", b =>
                 {
                     b.HasOne("JobsMedical.Web.Models.User", "Doctor")