feat: add portfolio ownership model, auth guards, and migration

tests/test_portfolio_comments.py

@@ -50,7 +50,9 @@ class FakeRepo:
                 setattr(portfolio, key, value)
         return portfolio
 
-    def list_portfolios(self, *, broker=None, status=None):
+    def list_portfolios(self, *, broker=None, status=None, owner_user_id=None):
+        if owner_user_id is not None and self._portfolio and self._portfolio.owner_user_id != owner_user_id:
+            return []
         return [self._portfolio] if self._portfolio else []
 
     def get_or_create_strategy_set(self, name: str, config: str) -> StrategySet:
@@ -181,6 +183,7 @@ def _portfolio() -> Portfolio:
         status="enabled",
         name="Samsung Electronics",
         symbol="005930",
+        owner_user_id="legacy-owner",
         cash_balance=1_000_000.0,
         asset_quantity=1.0,
         price=70_000.0,