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/__init__.py

@@ -0,0 +1,10 @@
+from application.forecast import ForecastError, ForecastService
+from application.scenarios import DEFAULT_SCENARIOS, ScenarioError, ScenarioService
+
+__all__ = [
+    "ForecastService",
+    "ForecastError",
+    "ScenarioService",
+    "ScenarioError",
+    "DEFAULT_SCENARIOS",
+]