CREATE TABLE IF NOT EXISTS budgets (
  id SERIAL PRIMARY KEY,
  owner_id INTEGER NOT NULL REFERENCES participants(id),
  category TEXT NOT NULL,
  month DATE NOT NULL,
  amount_limit NUMERIC(10,2) NOT NULL,
  created_at TIMESTAMPTZ DEFAULT NOW(),
  updated_at TIMESTAMPTZ DEFAULT NOW(),
  UNIQUE(owner_id, category, month)
);
CREATE INDEX IF NOT EXISTS idx_budgets_owner_month ON budgets(owner_id, month);