Add lifetime income/expense totals to UserBalance

New get_user_lifetime_totals_bql() runs tag-filtered BQL queries
(Payable + expense-entry, Receivable + income-entry) to compute
per-user lifetime totals separately from the net balance. Plumbed
through /api/v1/balance and /api/v1/balance/{user_id}; existing
clients keep working (fields default to zero / empty dict).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

models.py

@@ -90,6 +90,11 @@ class UserBalance(BaseModel):
     balance: int  # positive = libra owes user, negative = user owes libra
     accounts: list[Account] = []
     fiat_balances: dict[str, Decimal] = {}  # e.g. {"EUR": Decimal("250.0"), "USD": Decimal("100.0")}
+    # Lifetime totals (original entries only; not net of reconciliation)
+    total_expenses_sats: int = 0
+    total_expenses_fiat: dict[str, Decimal] = {}
+    total_income_sats: int = 0
+    total_income_fiat: dict[str, Decimal] = {}
 
 
 class ExpenseEntry(BaseModel):