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.

pyproject.toml

@@ -14,10 +14,10 @@ dependencies = [
 ]
 
 [project.scripts]
-cf = "cli.main:app"
+cf = "infrastructure.cli.main:app"
 
 [tool.setuptools.packages.find]
-include = ["cashflow_model*", "sync*", "engine*", "ai*", "cli*"]
+include = ["domain*", "application*", "infrastructure*"]
 
 [tool.ruff]
 target-version = "py311"