Stabilize core correctness and sync project plan state

tests/conftest.py

@@ -1,11 +1,14 @@
 """pytest configuration and shared fixtures."""
 
 import os
+import sys
 import tempfile
 from pathlib import Path
 
 import pytest
 
+sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "src"))
+
 # Default test data directory — overridden per-test by fixtures
 _default_test_dir = tempfile.mkdtemp(prefix="atocore_test_")
 os.environ["ATOCORE_DATA_DIR"] = _default_test_dir