Stop periscope/src importing PinScope validate.py after live C2 smoke.

PCB review and src checks use native parse, constraints lookup, and
review_session. Inherited validate.py and validation_tools.py stay in
dependency/.

tests/test_datasheet_excerpt_tool.py

@@ -12,14 +12,14 @@ from pypdf import PdfWriter
 
 from backend.periscopex.models import DesignGraph
 from backend.periscopex.utils import safe_mpn
-from backend.periscopex.validation_tools import (
+from backend.periscopex.review_tools import (
     EXCERPT_TOPICS,
     ExcerptState,
     execute_tool,
     get_datasheet_excerpt,
 )
 from backend.services.llm.types import PdfBlock
-from backend.services.validation import _signal_neighbors
+from backend.services.review_session import _signal_neighbors
 
 GRAPH = SIMPLE_PROJECT / "design_graph.json"
 IC_MPNS = {