Tighten PCB findings: actions, stitch gating, real copper.

Fill action on every finding and show it in the report. Stitch/return only
on large HS/power nets. Parse stackup thickness, arcs, and vias from the
board. IC courtyard pad copper is not PE-PLC-004 RULE. Recommended RC/cap
stay REVIEW.

backend/periscopex/placement_check.py

@@ -289,9 +289,15 @@ def _keepout_finding(ref, comp, cons, rule, graph: DesignGraph, layout: LayoutGr
     own = _net_for_pin(graph, ref, pin_no) if pin_no else None
     if not own:
         return []
+    pad_nets = [
+        p.net for p in fp.pads
+        if p.net
+    ]
     foreign: list[str] = []
     for s in layout.segments:
-        if not s.net or s.net == own:
+        if not s.net or kicad_nets_match(s.net, own):
+            continue
+        if any(kicad_nets_match(s.net, pn) for pn in pad_nets):
             continue
         if _in_poly(s.start[0], s.start[1], fp.courtyard) or _in_poly(
             s.end[0], s.end[1], fp.courtyard
@@ -300,17 +306,32 @@ def _keepout_finding(ref, comp, cons, rule, graph: DesignGraph, layout: LayoutGr
     if not foreign:
         return []
     net = sorted(set(foreign))[0]
+    is_crystal = comp.component_type == ComponentType.CRYSTAL
+    rec = (
+        "Keep unrelated nets out of the keepout if the datasheet shows a "
+        "keep-out zone; traces to this part's own pads are normal copper."
+    )
     return [Finding(
         designator=ref,
         mpn=comp.mpn or cons.mpn,
         aspect="placement",
         finding=f"Track on {net} enters courtyard of {ref} (keepout on {own}).",
+        facts=f"Segment on '{net}' has an endpoint inside {ref} courtyard.",
+        requirement="layout_rules kind=keepout (recommended courtyard isolation).",
+        inference=(
+            "Crystal keepout may apply."
+            if is_crystal
+            else "Not a pad net of this footprint — review, not a mandatory DRC."
+        ),
         why="layout_rules kind=keepout.",
-        status="WARNING",
-        recommendation="Keep other nets out of the courtyard.",
+        status="WARNING" if is_crystal else "INFO",
+        recommendation=rec,
+        action=rec,
         source="placement_check",
         rule_id="PE-PLC-004",
+        finding_class="REVIEW",
+        provenance="RECOMMENDED",
         net=net,
-        pins=[pin_no],
+        pins=[pin_no] if pin_no else [],
         source_page=rule.get("source_page"),
     )]