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/finding_engine.py

@@ -7,6 +7,7 @@ never becomes ERROR. LLM output is REVIEW, never RULE.
 
 from __future__ import annotations
 
+import logging
 from datetime import datetime, timezone
 from typing import Any, Iterable, Literal
 
@@ -14,6 +15,11 @@ from pydantic import BaseModel
 
 from backend.periscopex.models import Finding
 
+log = logging.getLogger(__name__)
+
+_STATUS_ORDER = {"ERROR": 0, "WARNING": 1, "INFO": 2}
+_CLASS_ORDER = {"RULE": 0, "RISK": 1, "REVIEW": 2, "INFO": 3}
+
 Provenance = Literal["MANDATORY", "RECOMMENDED", "TYPICAL", "EXAMPLE"]
 FindingClass = Literal["RULE", "RISK", "REVIEW", "INFO"]
 EvidenceStatus = Literal["SUFFICIENT", "INSUFFICIENT"]
@@ -256,9 +262,31 @@ def complete_finding(f: Finding) -> Finding:
     return f
 
 
+def sort_findings(findings: list[Finding]) -> list[Finding]:
+    """ERROR then WARNING then INFO; within that RULE > RISK > REVIEW > INFO."""
+    findings.sort(
+        key=lambda f: (
+            _STATUS_ORDER.get(f.status or "INFO", 9),
+            _CLASS_ORDER.get(f.finding_class or "INFO", 9),
+            f.designator or "",
+            f.rule_id or "",
+            f.finding or "",
+        )
+    )
+    return findings
+
+
 def complete_findings(findings: list[Finding]) -> None:
     for f in findings:
-        complete_finding(f)
+        try:
+            complete_finding(f)
+        except Exception:
+            log.exception(
+                "complete_finding failed for %s/%s",
+                getattr(f, "designator", "?"),
+                getattr(f, "rule_id", None),
+            )
+    sort_findings(findings)
 
 
 def apply_decisions(