feat: rate limit emails to two per address per hour

Foxnouns.Backend/Database/Migrations/20241211193653_AddSentEmailCache.cs

@@ -0,0 +1,53 @@
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+using NodaTime;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+
+#nullable disable
+
+namespace Foxnouns.Backend.Database.Migrations
+{
+    /// <inheritdoc />
+    [DbContext(typeof(DatabaseContext))]
+    [Migration("20241211193653_AddSentEmailCache")]
+    public partial class AddSentEmailCache : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "sent_emails",
+                columns: table => new
+                {
+                    id = table
+                        .Column<int>(type: "integer", nullable: false)
+                        .Annotation(
+                            "Npgsql:ValueGenerationStrategy",
+                            NpgsqlValueGenerationStrategy.IdentityByDefaultColumn
+                        ),
+                    email = table.Column<string>(type: "text", nullable: false),
+                    sent_at = table.Column<Instant>(
+                        type: "timestamp with time zone",
+                        nullable: false
+                    ),
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("pk_sent_emails", x => x.id);
+                }
+            );
+
+            migrationBuilder.CreateIndex(
+                name: "ix_sent_emails_email_sent_at",
+                table: "sent_emails",
+                columns: new[] { "email", "sent_at" }
+            );
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(name: "sent_emails");
+        }
+    }
+}