feat(expense): add controllers + register services

Adds ExpenseCategoriesController, ExpensesController, MonthlyStatementsController
and registers IExpenseCategoryService, IExpenseService, IMonthlyStatementService in DI.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

API/ROLAC.API/Controllers/MonthlyStatementsController.cs

@@ -0,0 +1,48 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using ROLAC.API.DTOs.Expense;
+using ROLAC.API.Services;
+
+namespace ROLAC.API.Controllers;
+
+[ApiController]
+[Route("api/monthly-statements")]
+[Authorize(Roles = "finance,super_admin")]
+public class MonthlyStatementsController : ControllerBase
+{
+    private readonly IMonthlyStatementService _svc;
+    public MonthlyStatementsController(IMonthlyStatementService svc) => _svc = svc;
+
+    [HttpGet]
+    public async Task<IActionResult> GetAll([FromQuery] int? year = null)
+        => Ok(await _svc.GetAllAsync(year));
+
+    [HttpGet("{id:int}")]
+    public async Task<IActionResult> GetById(int id)
+    {
+        var dto = await _svc.GetByIdAsync(id);
+        return dto is null ? NotFound() : Ok(dto);
+    }
+
+    [HttpPost]
+    public async Task<IActionResult> Create([FromBody] CreateMonthlyStatementRequest r)
+    {
+        try { return Ok(new { id = await _svc.CreateAsync(r) }); }
+        catch (InvalidOperationException ex) { return Conflict(new { message = ex.Message }); }
+    }
+
+    [HttpPut("{id:int}")]
+    public async Task<IActionResult> Update(int id, [FromBody] UpdateMonthlyStatementRequest r)
+    {
+        try { await _svc.UpdateAsync(id, r); return NoContent(); }
+        catch (KeyNotFoundException) { return NotFound(); }
+        catch (InvalidOperationException ex) { return Conflict(new { message = ex.Message }); }
+    }
+
+    [HttpPost("{id:int}/finalize")]
+    public async Task<IActionResult> Finalize(int id)
+    {
+        try { await _svc.FinalizeAsync(id); return NoContent(); }
+        catch (KeyNotFoundException) { return NotFound(); }
+    }
+}