T5: Dependency Injection — services через composition root

- AssistantService теперь принимает ForecastService в конструкторе
  (раньше создавал new ForecastService() внутри analyze/advice)
- infrastructure/cli/main.py: _build_services() — composition root,
  собирает граф ForecastService, ScenarioService, AssistantService, CurrencyConverter
- Все CLI-команды используют _build_services(model) вместо прямого new
- test_ai.py: обновлён под новый контракт AssistantService

Tests: 67/67 pass.

infrastructure/ai/assistant.py

@@ -23,17 +23,18 @@ class AssistantService:
     def __init__(
         self,
         model: FinancialModel,
+        forecast_service: ForecastService,
         converter: CurrencyConverter | None = None,
         display_currency: str | None = None,
     ):
         self.model = model
+        self.forecast_service = forecast_service
         self.converter = converter or CurrencyConverter(model.exchange_rates)
         self.display_currency = display_currency or model.base_currency
 
     def analyze(self, months: int = 12) -> dict:
-        forecast_service = ForecastService(self.model)
-        forecast_result = forecast_service.forecast_cashflow(months)
-        summary = forecast_service.summary(months)
+        forecast_result = self.forecast_service.forecast_cashflow(months)
+        summary = self.forecast_service.summary(months)
 
         prompt = prompts.format_context(
             model_json=json.dumps(self.model.to_dict(), indent=2, ensure_ascii=False, cls=_DecimalEncoder),
@@ -51,8 +52,7 @@ class AssistantService:
         }
 
     def advice(self, question: str, months: int = 12) -> dict:
-        forecast_service = ForecastService(self.model)
-        forecast_result = forecast_service.forecast_cashflow(months)
+        forecast_result = self.forecast_service.forecast_cashflow(months)
 
         prompt = prompts.ADVICE_PROMPT.format(
             model_json=json.dumps(self.model.to_dict(), indent=2, ensure_ascii=False, cls=_DecimalEncoder),