T1: restructure to domain/application/infrastructure + schema version 1

- Move cashflow_model/ -> domain/
- Move engine/ -> application/
- Move cli/, sync/, ai/ -> infrastructure/
- Update all imports across codebase and tests
- Add version=1 to FinancialModel.to_dict() with migration hook in from_dict
- Update pyproject.toml: cf entry point and packages.find

Tests: 63/63 pass.

application/forecast.py

@@ -0,0 +1,103 @@
+from copy import deepcopy
+
+from domain import Account, FinancialModel
+
+
+class ForecastError(Exception):
+    pass
+
+
+class ForecastService:
+    def __init__(self, model: FinancialModel):
+        self.model = deepcopy(model)
+
+    def forecast_cashflow(self, months: int = 12) -> list[dict]:
+        if months < 1:
+            raise ForecastError("months must be >= 1")
+
+        results = []
+        for account in self.model.accounts:
+            monthly = self._project_account(account, months)
+            for m in range(months):
+                results.append({
+                    "account": account.name,
+                    "month": m + 1,
+                    "balance": monthly[m]["balance"],
+                    "income": monthly[m]["income"],
+                    "expenses": monthly[m]["expenses"],
+                })
+
+        # Asset growth — once per month, distributed across accounts proportionally
+        for m in range(months):
+            total_growth = sum(
+                a.value * a.growth_rate / 100 / 12
+                for a in self.model.assets
+            )
+            month_rows = [r for r in results if r["month"] == m + 1]
+            total_bal = sum(r["balance"] for r in month_rows) or 1
+            for r in month_rows:
+                share = r["balance"] / total_bal
+                r["income"] = round(r["income"] + total_growth * share, 2)
+                r["balance"] = round(r["balance"] + total_growth * share, 2)
+
+            # Compound asset values for next month
+            for a in self.model.assets:
+                a.value += a.value * a.growth_rate / 100 / 12
+
+        return results
+
+    def _project_account(self, account: Account, months: int) -> list[dict]:
+        balance = account.balance
+        monthly = []
+        for m in range(months):
+            income = 0.0
+            expenses = 0.0
+
+            for t in self.model.transactions:
+                if t.account == str(account.id):
+                    if t.amount > 0:
+                        income += t.amount
+                    else:
+                        expenses += abs(t.amount)
+
+            for r in self.model.recurring:
+                if r.amount > 0:
+                    income += r.amount
+                else:
+                    expenses += abs(r.amount)
+
+            expenses += self._liability_cost(account)
+
+            balance += income - expenses
+
+            monthly.append({
+                "balance": round(balance, 2),
+                "income": round(income, 2),
+                "expenses": round(expenses, 2),
+            })
+        return monthly
+
+    def _liability_cost(self, account: Account) -> float:
+        total = 0.0
+        for liability in self.model.liabilities:
+            interest_cost = liability.balance * liability.interest / 100 / 12
+            total += interest_cost
+            liability.balance -= liability.payment - interest_cost
+            if liability.balance < 0:
+                liability.balance = 0
+        return total
+
+    def summary(self, months: int = 12) -> dict:
+        results = self.forecast_cashflow(months)
+        if not results:
+            return {"total_balance": 0, "total_income": 0, "total_expenses": 0, "months": months}
+
+        final = results[-1]
+        all_income = sum(r["income"] for r in results)
+        all_expenses = sum(r["expenses"] for r in results)
+        return {
+            "total_balance": final["balance"],
+            "total_income": round(all_income, 2),
+            "total_expenses": round(all_expenses, 2),
+            "months": months,
+        }