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/conftest.py

@@ -10,8 +10,14 @@ import pytest
 # Ensure the repo root is on sys.path so `import backend.*` works whether
 # pytest is invoked from the repo root or a subdirectory.
 REPO_ROOT = Path(__file__).resolve().parents[1]
-if str(REPO_ROOT) not in sys.path:
-    sys.path.insert(0, str(REPO_ROOT))
+for p in (
+    REPO_ROOT / "periscope" / "dependency",
+    REPO_ROOT / "periscope" / "src",
+    REPO_ROOT,
+):
+    s = str(p)
+    if p.is_dir() and s not in sys.path:
+        sys.path.insert(0, s)
 
 from backend.vendor_path import ensure_impedancefinder