feat(#17): CRUD de categorias — API Go + tela Vue + testes unitários

API REST /api/categories (GET/POST/PUT/DELETE) com regras de negócio:
categorias padrão não podem ser excluídas; categorias com transações vinculadas
também bloqueadas. Tela Vue com formulário inline de criação/edição, indicador
visual de categorias padrão e botão de exclusão condicional.

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

apps/api/internal/repository/category.go

@@ -0,0 +1,106 @@
+package repository
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"financeiro-carvalho/internal/model"
+)
+
+var ErrNotFound = errors.New("not found")
+
+type CategoryRepository interface {
+	List(ctx context.Context) ([]model.Category, error)
+	GetByID(ctx context.Context, id int) (*model.Category, error)
+	Create(ctx context.Context, name, color string) (*model.Category, error)
+	Update(ctx context.Context, id int, name, color string) (*model.Category, error)
+	Delete(ctx context.Context, id int) error
+	HasTransactions(ctx context.Context, id int) (bool, error)
+}
+
+type categoryRepo struct{ db *pgxpool.Pool }
+
+func NewCategoryRepository(db *pgxpool.Pool) CategoryRepository {
+	return &categoryRepo{db: db}
+}
+
+func (r *categoryRepo) List(ctx context.Context) ([]model.Category, error) {
+	rows, err := r.db.Query(ctx, `
+		SELECT id, name, color, is_default, created_at, updated_at
+		FROM categories
+		ORDER BY is_default DESC, name ASC`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var out []model.Category
+	for rows.Next() {
+		var c model.Category
+		if err := rows.Scan(&c.ID, &c.Name, &c.Color, &c.IsDefault, &c.CreatedAt, &c.UpdatedAt); err != nil {
+			return nil, err
+		}
+		out = append(out, c)
+	}
+	return out, rows.Err()
+}
+
+func (r *categoryRepo) GetByID(ctx context.Context, id int) (*model.Category, error) {
+	var c model.Category
+	err := r.db.QueryRow(ctx, `
+		SELECT id, name, color, is_default, created_at, updated_at
+		FROM categories WHERE id = $1`, id).
+		Scan(&c.ID, &c.Name, &c.Color, &c.IsDefault, &c.CreatedAt, &c.UpdatedAt)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	return &c, err
+}
+
+func (r *categoryRepo) Create(ctx context.Context, name, color string) (*model.Category, error) {
+	var c model.Category
+	err := r.db.QueryRow(ctx, `
+		INSERT INTO categories (name, color)
+		VALUES ($1, $2)
+		RETURNING id, name, color, is_default, created_at, updated_at`,
+		name, color).
+		Scan(&c.ID, &c.Name, &c.Color, &c.IsDefault, &c.CreatedAt, &c.UpdatedAt)
+	return &c, err
+}
+
+func (r *categoryRepo) Update(ctx context.Context, id int, name, color string) (*model.Category, error) {
+	var c model.Category
+	err := r.db.QueryRow(ctx, `
+		UPDATE categories
+		SET name = $1, color = $2, updated_at = NOW()
+		WHERE id = $3
+		RETURNING id, name, color, is_default, created_at, updated_at`,
+		name, color, id).
+		Scan(&c.ID, &c.Name, &c.Color, &c.IsDefault, &c.CreatedAt, &c.UpdatedAt)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	return &c, err
+}
+
+func (r *categoryRepo) Delete(ctx context.Context, id int) error {
+	tag, err := r.db.Exec(ctx, `DELETE FROM categories WHERE id = $1`, id)
+	if err != nil {
+		return err
+	}
+	if tag.RowsAffected() == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+func (r *categoryRepo) HasTransactions(ctx context.Context, id int) (bool, error) {
+	var count int
+	err := r.db.QueryRow(ctx,
+		`SELECT COUNT(*) FROM transactions WHERE category_id = $1`, id).
+		Scan(&count)
+	return count > 0, err
+}