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/repository/dashboard.go

@@ -0,0 +1,122 @@
+package repository
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"financeiro-carvalho/internal/model"
+)
+
+type DashboardRepository struct {
+	pool *pgxpool.Pool
+}
+
+func NewDashboardRepository(pool *pgxpool.Pool) *DashboardRepository {
+	return &DashboardRepository{pool: pool}
+}
+
+func (r *DashboardRepository) MonthlySummary(ctx context.Context, month string) (income, expenses float64, err error) {
+	row := r.pool.QueryRow(ctx, `
+		SELECT
+			COALESCE(SUM(CASE WHEN type = 'income'  THEN amount ELSE 0 END), 0),
+			COALESCE(SUM(CASE WHEN type = 'expense' THEN amount ELSE 0 END), 0)
+		FROM transactions
+		WHERE to_char(date, 'YYYY-MM') = $1
+	`, month)
+	err = row.Scan(&income, &expenses)
+	return
+}
+
+func (r *DashboardRepository) ByCategory(ctx context.Context, month string) ([]model.CategoryTotal, error) {
+	rows, err := r.pool.Query(ctx, `
+		SELECT
+			t.category_id,
+			COALESCE(c.name,  'Sem categoria') AS category_name,
+			COALESCE(c.color, '#6B7280')       AS color,
+			SUM(t.amount)                      AS total
+		FROM transactions t
+		LEFT JOIN categories c ON c.id = t.category_id
+		WHERE to_char(t.date, 'YYYY-MM') = $1
+		  AND t.type = 'expense'
+		GROUP BY t.category_id, c.name, c.color
+		ORDER BY total DESC
+	`, month)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var out []model.CategoryTotal
+	for rows.Next() {
+		var ct model.CategoryTotal
+		if err := rows.Scan(&ct.CategoryID, &ct.CategoryName, &ct.Color, &ct.Total); err != nil {
+			return nil, err
+		}
+		out = append(out, ct)
+	}
+	return out, rows.Err()
+}
+
+func (r *DashboardRepository) MonthlyEvolution(ctx context.Context, month string) ([]model.MonthEvolution, error) {
+	rows, err := r.pool.Query(ctx, `
+		SELECT
+			to_char(m.ms, 'YYYY-MM')                                                  AS month,
+			COALESCE(SUM(CASE WHEN t.type = 'income'  THEN t.amount ELSE 0 END), 0)  AS income,
+			COALESCE(SUM(CASE WHEN t.type = 'expense' THEN t.amount ELSE 0 END), 0)  AS expenses
+		FROM generate_series(
+			date_trunc('month', ($1 || '-01')::date) - INTERVAL '5 months',
+			date_trunc('month', ($1 || '-01')::date),
+			'1 month'::interval
+		) AS m(ms)
+		LEFT JOIN transactions t ON date_trunc('month', t.date) = m.ms
+		GROUP BY m.ms
+		ORDER BY m.ms
+	`, month)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var out []model.MonthEvolution
+	for rows.Next() {
+		var me model.MonthEvolution
+		if err := rows.Scan(&me.Month, &me.Income, &me.Expenses); err != nil {
+			return nil, err
+		}
+		me.Saved = me.Income - me.Expenses
+		out = append(out, me)
+	}
+	return out, rows.Err()
+}
+
+func (r *DashboardRepository) RecentTransactions(ctx context.Context, month string) ([]model.RecentTransaction, error) {
+	rows, err := r.pool.Query(ctx, `
+		SELECT
+			t.id,
+			t.date::text,
+			t.description,
+			COALESCE(c.name, 'Sem categoria') AS category_name,
+			t.amount,
+			t.type
+		FROM transactions t
+		LEFT JOIN categories c ON c.id = t.category_id
+		WHERE to_char(t.date, 'YYYY-MM') = $1
+		ORDER BY t.date DESC, t.id DESC
+		LIMIT 10
+	`, month)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var out []model.RecentTransaction
+	for rows.Next() {
+		var rt model.RecentTransaction
+		if err := rows.Scan(&rt.ID, &rt.Date, &rt.Description, &rt.CategoryName, &rt.Amount, &rt.Type); err != nil {
+			return nil, err
+		}
+		out = append(out, rt)
+	}
+	return out, rows.Err()
+}