PortfolioGoal is domain vocabulary (a Scenario's goal — legacy planning branches
on PortfolioGoal.INCREASING_EPC), so it belongs in domain/ co-located with
scenario.py, mirroring how domain/epc/wall_type.py holds an enum that
infrastructure/ imports. This lets the consolidated ScenarioModel (next slice)
source the goal enum from domain without an infra→backend dependency.
portfolio.py keeps a re-export so every existing
`from ...portfolio import PortfolioGoal` caller is unaffected.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
