feat(#35): rendimento CDI automático em contas de investimento

- Migration 010: colunas yield_type e last_yield_date em accounts + source='yield' nas transações
- CDIYieldService: busca taxas BCB (serie 12) e cria transação source=yield com rendimento acumulado
- Weekends/feriados sem taxa usam última taxa disponível (AC4)
- GET /api/accounts dispara cálculo CDI on-demand antes de retornar saldos
- AccountsView: seletor yield_type (none/cdi/variable) + badge CDI/VAR na listagem
- Transações source=yield aparecem no histórico com descrição 'Rendimento CDI — {período}'

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

apps/api/internal/service/cdi.go

@@ -0,0 +1,139 @@
+package service
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"financeiro-carvalho/internal/model"
+	"financeiro-carvalho/internal/repository"
+)
+
+const bcbCDIURL = "https://api.bcb.gov.br/dados/serie/bcdata.sgs.12/dados?formato=json&dataInicial=%s&dataFinal=%s"
+
+type CDIYieldService struct {
+	accountRepo repository.AccountRepoWithYield
+	txRepo      repository.ManualTransactionRepository
+	client      *http.Client
+}
+
+func NewCDIYieldService(accountRepo repository.AccountRepoWithYield, txRepo repository.ManualTransactionRepository) *CDIYieldService {
+	return &CDIYieldService{
+		accountRepo: accountRepo,
+		txRepo:      txRepo,
+		client:      &http.Client{Timeout: 10 * time.Second},
+	}
+}
+
+// ApplyYield fetches CDI rates and creates a yield transaction for the account if applicable.
+func (s *CDIYieldService) ApplyYield(ctx context.Context, a *model.Account) error {
+	if a.YieldType != "cdi" {
+		return nil
+	}
+
+	// Determine the start date (day after last yield)
+	yesterday := time.Now().AddDate(0, 0, -1).Format("2006-01-02")
+	startDate := a.CreatedAt[:10] // default: account creation date
+	if a.LastYieldDate != nil && *a.LastYieldDate != "" {
+		startDate = *a.LastYieldDate
+		// start is exclusive: add one day
+		t, err := time.Parse("2006-01-02", startDate)
+		if err != nil {
+			return nil
+		}
+		startDate = t.AddDate(0, 0, 1).Format("2006-01-02")
+	}
+
+	if startDate > yesterday {
+		// nothing to calculate yet
+		return nil
+	}
+
+	rates, err := s.fetchCDIRates(startDate, yesterday)
+	if err != nil {
+		// BCB API unreachable — skip silently; will retry next load
+		return nil
+	}
+	if len(rates) == 0 {
+		return nil
+	}
+
+	// Fill gaps (weekends/holidays) using last known rate
+	rateMap := make(map[string]float64, len(rates))
+	for _, r := range rates {
+		rateMap[r.date] = r.value
+	}
+
+	compound := 1.0
+	lastRate := rates[0].value
+	start, _ := time.Parse("2006-01-02", startDate)
+	end, _ := time.Parse("2006-01-02", yesterday)
+	for d := start; !d.After(end); d = d.AddDate(0, 0, 1) {
+		key := d.Format("2006-01-02")
+		if r, ok := rateMap[key]; ok {
+			lastRate = r
+		}
+		compound *= 1 + lastRate/100
+	}
+
+	yieldAmount := a.Balance * (compound - 1)
+	if yieldAmount <= 0 {
+		return nil
+	}
+
+	period := fmt.Sprintf("%s → %s", startDate, yesterday)
+	tx := model.Transaction{
+		Date:        time.Now().Format("2006-01-02"),
+		Amount:      yieldAmount,
+		Description: fmt.Sprintf("Rendimento CDI — %s", period),
+		Type:        "income",
+		Source:      "yield",
+		AccountID:   &a.ID,
+	}
+	if _, err := s.txRepo.Create(ctx, tx); err != nil {
+		return err
+	}
+
+	return s.accountRepo.UpdateLastYieldDate(ctx, a.ID, yesterday)
+}
+
+type bcbEntry struct {
+	date  string
+	value float64
+}
+
+func (s *CDIYieldService) fetchCDIRates(startDate, endDate string) ([]bcbEntry, error) {
+	// BCB API uses DD/MM/YYYY format
+	start, _ := time.Parse("2006-01-02", startDate)
+	end, _ := time.Parse("2006-01-02", endDate)
+	url := fmt.Sprintf(bcbCDIURL, start.Format("02/01/2006"), end.Format("02/01/2006"))
+
+	resp, err := s.client.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	var raw []struct {
+		Data  string `json:"data"`
+		Valor string `json:"valor"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&raw); err != nil {
+		return nil, err
+	}
+
+	var out []bcbEntry
+	for _, r := range raw {
+		// BCB date format: DD/MM/YYYY → convert to YYYY-MM-DD
+		t, err := time.Parse("02/01/2006", r.Data)
+		if err != nil {
+			continue
+		}
+		var v float64
+		fmt.Sscanf(r.Valor, "%f", &v)
+		out = append(out, bcbEntry{date: t.Format("2006-01-02"), value: v})
+	}
+	return out, nil
+}