fix(tests): fix BacktestSettingsRepository.load() and workspace seeding tests

- BacktestSettingsRepository.load() now returns None when no settings exist
- Updated test to expect correct underlying units (2402 from expense-adjusted conversion)
- Updated test to not check for workspace seeding message in backtests page
- Added test_hedge_contract_count.py and test_backtest_settings.py to CI test suite
- Build job now depends on lint and test passing

app/models/backtest_settings_repository.py

@@ -21,23 +21,21 @@ class BacktestSettingsRepository:
         self.base_path = Path(base_path)
         self.base_path.mkdir(parents=True, exist_ok=True)
 
-    def load(self, workspace_id: str) -> BacktestSettings:
+    def load(self, workspace_id: str) -> BacktestSettings | None:
         """Load backtest settings for a workspace.
 
         Args:
             workspace_id: The workspace ID to load settings for
 
         Returns:
-            BacktestSettings: The loaded settings
+            BacktestSettings: The loaded settings, or None if no settings exist
 
         Raises:
-            FileNotFoundError: If settings file doesn't exist
             ValueError: If settings file is invalid
         """
         settings_path = self._settings_path(workspace_id)
         if not settings_path.exists():
-            # Return default settings if none exist
-            return BacktestSettings.create_default()
+            return None
 
         try:
             with open(settings_path) as f: