feat: complete fase 1 - all controllers, services, middleware

- Added Ejecutivo.cs entity
- ArqueoService + ArqueoController (arqueos por fecha/usuario)
- 13 missing controllers: Curso, Descuento, Documento, Empresa, Horario,
  Jornada, Programa, Propuesta, Region, Sala, Sede, Tarifa, Usuario
- JwtMiddleware.cs for cookie/token validation
- SpComplexQueries.cs for Dapper multi-resultset
- ArqueoService registered in DI
- Build: 0 errors
- Total: 21 controllers, 8 services, 7 repos, 21 entities

backend/src/Ventas.API/Controllers/DescuentoController.cs

@@ -0,0 +1,49 @@
+using Dapper;
+using Npgsql;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Ventas.API.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+[Authorize]
+public class DescuentoController : ControllerBase
+{
+    private readonly string _connectionString;
+
+    public DescuentoController(IConfiguration configuration)
+    {
+        _connectionString = configuration.GetConnectionString("Default")!;
+    }
+
+    [HttpGet]
+    public async Task<IActionResult> Buscar([FromQuery] string tipoBusqueda, [FromQuery] int sede, [FromQuery] int programa, [FromQuery] int horario)
+    {
+        using var connection = new NpgsqlConnection(_connectionString);
+        var rows = await connection.QueryAsync("sige_sam_v3.BuscarDescuentos",
+            new { tipobusqueda = tipoBusqueda, sedeid = sede, programaid = programa, horarioid = horario },
+            commandType: System.Data.CommandType.StoredProcedure);
+        return Ok(rows.Select(r => (Dictionary<string, object>)(IDictionary<string, object>)r!));
+    }
+
+    [HttpGet("summer")]
+    public async Task<IActionResult> Summer([FromQuery] int cantidadCursos)
+    {
+        using var connection = new NpgsqlConnection(_connectionString);
+        var rows = await connection.QueryAsync("sige_sam_v3.BuscarDesctoSummer",
+            new { cantidad = cantidadCursos },
+            commandType: System.Data.CommandType.StoredProcedure);
+        return Ok(rows.Select(r => (Dictionary<string, object>)(IDictionary<string, object>)r!));
+    }
+
+    [HttpPost]
+    public async Task<IActionResult> Ingresar([FromQuery] int cotizacionId, [FromQuery] int descuentoId, [FromQuery] int tipoDescuento, [FromQuery] int nuevoMonto)
+    {
+        using var connection = new NpgsqlConnection(_connectionString);
+        await connection.ExecuteAsync("sige_sam_v3.DescuentoCotizacion",
+            new { cotiid = cotizacionId, desctoid = descuentoId, tipoid = tipoDescuento, nuevototal = nuevoMonto },
+            commandType: System.Data.CommandType.StoredProcedure);
+        return Ok(new { mensaje = "ok" });
+    }
+}