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.

frontend/src/lib/utils.ts

@@ -1,6 +1,6 @@
 import { clsx, type ClassValue } from "clsx"
 import { twMerge } from "tailwind-merge"
-import type { Finding, FindingStatus } from "./types";
+import type { Finding, FindingClass, FindingStatus } from "./types";
 
 export function cn(...inputs: ClassValue[]) {
   return twMerge(clsx(inputs))
@@ -16,9 +16,19 @@ export function groupBy<T>(items: T[], key: (item: T) => string): Record<string,
 }
 
 const STATUS_ORDER: Record<FindingStatus, number> = { ERROR: 0, WARNING: 1, INFO: 2 };
+const CLASS_ORDER: Record<FindingClass, number> = { RULE: 0, RISK: 1, REVIEW: 2, INFO: 3 };
 
 export function sortFindings(findings: Finding[]): Finding[] {
-  return [...findings].sort((a, b) => STATUS_ORDER[a.status] - STATUS_ORDER[b.status]);
+  return [...findings].sort((a, b) => {
+    const status = STATUS_ORDER[a.status] - STATUS_ORDER[b.status];
+    if (status !== 0) return status;
+    const ac = CLASS_ORDER[a.finding_class ?? "INFO"] ?? 9;
+    const bc = CLASS_ORDER[b.finding_class ?? "INFO"] ?? 9;
+    if (ac !== bc) return ac - bc;
+    return (a.designator || "").localeCompare(b.designator || "")
+      || (a.rule_id || "").localeCompare(b.rule_id || "")
+      || (a.finding || "").localeCompare(b.finding || "");
+  });
 }
 
 export function getFindingKey(finding: Finding, index: number): string {