feat(api): add DashboardController with overview and monthly-trend endpoints

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

MoneyMap/Controllers/DashboardController.cs

@@ -0,0 +1,72 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using MoneyMap.Data;
+using MoneyMap.Services;
+
+namespace MoneyMap.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+public class DashboardController : ControllerBase
+{
+    private readonly IDashboardService _dashboardService;
+    private readonly MoneyMapContext _db;
+
+    public DashboardController(IDashboardService dashboardService, MoneyMapContext db)
+    {
+        _dashboardService = dashboardService;
+        _db = db;
+    }
+
+    [HttpGet]
+    public async Task<IActionResult> Get(
+        [FromQuery] int? topCategoriesCount = null,
+        [FromQuery] int? recentTransactionsCount = null)
+    {
+        var data = await _dashboardService.GetDashboardDataAsync(
+            topCategoriesCount ?? 8,
+            recentTransactionsCount ?? 20);
+
+        return Ok(data);
+    }
+
+    [HttpGet("monthly-trend")]
+    public async Task<IActionResult> MonthlyTrend(
+        [FromQuery] int? months = null,
+        [FromQuery] string? category = null)
+    {
+        var monthCount = months ?? 6;
+        var endDate = DateTime.Today;
+        var startDate = new DateTime(endDate.Year, endDate.Month, 1).AddMonths(-(monthCount - 1));
+
+        var q = _db.Transactions
+            .Where(t => t.Date >= startDate && t.Date <= endDate)
+            .Where(t => t.Amount < 0)
+            .Where(t => t.TransferToAccountId == null)
+            .ExcludeTransfers();
+
+        if (!string.IsNullOrWhiteSpace(category))
+            q = q.Where(t => t.Category == category);
+
+        var monthly = await q
+            .GroupBy(t => new { t.Date.Year, t.Date.Month })
+            .Select(g => new
+            {
+                Year = g.Key.Year,
+                Month = g.Key.Month,
+                Total = g.Sum(t => Math.Abs(t.Amount)),
+                Count = g.Count()
+            })
+            .OrderBy(x => x.Year).ThenBy(x => x.Month)
+            .ToListAsync();
+
+        var result = monthly.Select(m => new
+        {
+            Period = $"{m.Year}-{m.Month:D2}",
+            m.Total,
+            m.Count
+        }).ToList();
+
+        return Ok(new { Category = category ?? "All Spending", Months = result });
+    }
+}