feat(#20): dashboard financeiro mensal — 4 widgets + endpoint de agregação

Adiciona GET /api/dashboard?month=YYYY-MM com resumo mensal (% poupado,
gastos por categoria, evolução 6 meses, últimas 10 transações, recorrências
pendentes). HomeView.vue reescrita com 4 widgets e gráficos CSS nativos.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

apps/api/internal/handler/dashboard.go

@@ -0,0 +1,30 @@
+package handler
+
+import (
+	"net/http"
+	"time"
+
+	"financeiro-carvalho/internal/service"
+)
+
+type DashboardHandler struct {
+	svc *service.DashboardService
+}
+
+func NewDashboardHandler(svc *service.DashboardService) *DashboardHandler {
+	return &DashboardHandler{svc: svc}
+}
+
+func (h *DashboardHandler) Get(w http.ResponseWriter, r *http.Request) {
+	month := r.URL.Query().Get("month")
+	if month == "" {
+		month = time.Now().Format("2006-01")
+	}
+
+	data, err := h.svc.Get(r.Context(), month)
+	if err != nil {
+		respondError(w, http.StatusInternalServerError, "failed to load dashboard")
+		return
+	}
+	respondJSON(w, http.StatusOK, data)
+}