Split native Periscope (periscope/src) from inherited PinScope (periscope/dependency).

Keep validate.py and the finding engine as-is. AGPL LICENSE stays at the repo root.
Docker overlays dependency then src. Do not delete the inherited tree.

tests/test_placement_pack.py

@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+from tests.paths import SIMPLE_PROJECT, TAXONOMY
+
 from pathlib import Path
 
 from backend.periscopex.functional_groups import (
@@ -18,7 +20,7 @@ from backend.periscopex.models import (
 )
 from backend.periscopex.placement_pack import build_placement_pack
 
-SIMPLE = Path(__file__).resolve().parents[1] / "simple_project"
+SIMPLE = SIMPLE_PROJECT
 
 
 def _graph() -> DesignGraph: