feat: core entities, infrastructure, and lead repositories

- 25 domain entities mapped from original Datos/ classes
- 4 enums (EstadoLead, TipoPago, TipoDocumento, TipoDescuento)
- DTOs for Lead, Auth flows
- 6 repository interfaces
- VentasDbContext with EF Core + Npgsql
- LeadRepository (command SPs) and LeadQueryRepository (query SPs) with Dapper
- Program.cs with JWT auth, CORS, DI setup
- appsettings.json with connection string
- .gitignore for bin/obj/node_modules
- ROADMAP.md for daily progress tracking

backend/src/Ventas.API/Program.cs

@@ -0,0 +1,60 @@
+using System.Text;
+using Microsoft.AspNetCore.Authentication.JwtBearer;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.IdentityModel.Tokens;
+using Ventas.Infrastructure.Data;
+using Ventas.Infrastructure.Repositories;
+using Ventas.Core.Interfaces;
+
+var builder = WebApplication.CreateBuilder(args);
+
+var connectionString = builder.Configuration.GetConnectionString("Default")!;
+
+builder.Services.AddControllers();
+builder.Services.AddOpenApi();
+
+builder.Services.AddDbContext<VentasDbContext>(options =>
+    options.UseNpgsql(connectionString));
+
+builder.Services.AddScoped<ILeadRepository>(sp =>
+    new LeadRepository(connectionString));
+builder.Services.AddScoped<ILeadQueryRepository>(sp =>
+    new LeadQueryRepository(connectionString));
+
+var jwtSecret = builder.Configuration["Jwt:Secret"] ?? "default-dev-secret-change-in-production";
+builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
+    .AddJwtBearer(options =>
+    {
+        options.TokenValidationParameters = new TokenValidationParameters
+        {
+            ValidateIssuer = false,
+            ValidateAudience = false,
+            ValidateLifetime = true,
+            ValidateIssuerSigningKey = true,
+            IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(jwtSecret))
+        };
+    });
+
+builder.Services.AddCors(options =>
+{
+    options.AddDefaultPolicy(policy =>
+    {
+        policy.AllowAnyOrigin()
+              .AllowAnyHeader()
+              .AllowAnyMethod();
+    });
+});
+
+var app = builder.Build();
+
+if (app.Environment.IsDevelopment())
+{
+    app.MapOpenApi();
+}
+
+app.UseCors();
+app.UseAuthentication();
+app.UseAuthorization();
+app.MapControllers();
+
+app.Run();