ADR-002: Preserve Python domain and SQLite behavior

Status: Accepted

Context

This is a runtime-shell migration, not a redesign. Existing databases (schema v1–v4) and scoring semantics must keep working.

Decision

Port the scoring policy, ISO week logic, slug generation, and migration runner verbatim from the Tkinter app into backend/src/portfolio_manager/domain and .../infrastructure/db. Keep domain entities as dataclasses; use Pydantic only at the API/config boundary. Retain the sqlite3 repositories (no ORM).

Consequences

• Legacy databases open without manual conversion (verified by tests/compatibility/test_legacy_db.py).
• One intentional deviation: cancelled milestones are now excluded from the scoring denominator, per the SRS explicit rule (the Tkinter COUNT(*) counted them). Documented here and covered by tests.