Replace findings list with a tree; filter ESD/PI false positives.

PE-ESD-001 only on J* connector–IC nets (skip NC, unconnected, VSYS/GND/3V3).
PE-PI-001 treats any capacitor on the rail, including KiCad slash prefixes, as
decoupling. Sort findings ERROR then WARNING then INFO, then RULE/RISK/REVIEW/INFO.
Report sidebar is a collapsed expand-on-click tree instead of an all-open list.
GET /report and complete_findings fail-soft and sort the same way.

backend/periscopex/pcb_net_match.py

@@ -22,6 +22,21 @@ def normalize_kicad_hierarchy_net(name: str) -> str:
     return n
 
 
+def refs_on_matched_net(graph: DesignGraph, net_name: str) -> list[str]:
+    """Component refs on *net_name*, including KiCad ``/``-prefixed aliases."""
+    refs: set[str] = set()
+    if not net_name:
+        return []
+    for name, net in graph.nets.items():
+        if name == net_name or kicad_nets_match(name, net_name):
+            refs.update(pc.component_ref for pc in net.pins)
+    for ref, comp in graph.components.items():
+        for pin_net in comp.pins.values():
+            if pin_net and (pin_net == net_name or kicad_nets_match(pin_net, net_name)):
+                refs.add(ref)
+    return sorted(refs)
+
+
 def kicad_nets_match(a: str, b: str) -> bool:
     """True if schematic and PCB names are the same KiCad net.