대시보드 — 충전기별 에러코드 누적 순위 차트 추가

- /api/stats/charger-error-codes 엔드포인트 추가
  (Top 10 충전기 × Top 6 에러코드 stacked bar, 나머지 기타로 합산)
- dashboard.html: 에러코드 누적 순위 가로 스택 바 차트 카드 추가
  (클릭 시 해당 충전기 신고 목록으로 이동)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/main.py

@@ -540,3 +540,66 @@ def stats_top_chargers(limit: int = 10):
         ]
     finally:
         db.close()
+
+
+@app.get("/api/stats/charger-error-codes")
+def stats_charger_error_codes(charger_limit: int = 10, code_limit: int = 6):
+    """충전기별 에러코드 누적 건수 Top N (에러코드 입력된 신고 기준)."""
+    from database import SessionLocal
+    from sqlalchemy import text
+    from collections import defaultdict
+    db = SessionLocal()
+    try:
+        rows = db.execute(text("""
+            SELECT rep.charger_id,
+                   COALESCE(c.station_name, rep.charger_id) AS station_name,
+                   COALESCE(c.name, '') AS charger_name,
+                   TRIM(rep.error_code) AS error_code,
+                   COUNT(*) AS cnt
+            FROM reports rep
+            LEFT JOIN chargers c ON c.id = rep.charger_id
+            WHERE rep.error_code IS NOT NULL
+              AND TRIM(rep.error_code) != ''
+            GROUP BY rep.charger_id, c.station_name, c.name, TRIM(rep.error_code)
+        """)).fetchall()
+
+        if not rows:
+            return {"chargers": [], "error_codes": []}
+
+        charger_info = {}
+        code_totals = defaultdict(int)
+
+        for row in rows:
+            cid, sname, cname, ecode, cnt = row
+            cnt = int(cnt)
+            if cid not in charger_info:
+                charger_info[cid] = {"station_name": sname, "charger_name": cname,
+                                     "total": 0, "errors": {}}
+            charger_info[cid]["total"] += cnt
+            charger_info[cid]["errors"][ecode] = cnt
+            code_totals[ecode] += cnt
+
+        top_chargers = sorted(charger_info.items(), key=lambda x: -x[1]["total"])[:charger_limit]
+        top_codes    = [c for c, _ in sorted(code_totals.items(), key=lambda x: -x[1])[:code_limit]]
+
+        result = []
+        for cid, info in reversed(top_chargers):   # 역순: 차트에서 1위가 위에
+            label = info["station_name"]
+            if info["charger_name"]:
+                label += f" ({info['charger_name']})"
+            if len(label) > 22:
+                label = label[:20] + "…"
+            errors = info["errors"]
+            other  = sum(cnt for code, cnt in errors.items() if code not in top_codes)
+            entry  = {"charger_id": cid, "label": label, "total": info["total"]}
+            for code in top_codes:
+                entry[code] = errors.get(code, 0)
+            if other:
+                entry["기타"] = other
+            result.append(entry)
+
+        has_other = any(r.get("기타", 0) > 0 for r in result)
+        all_codes = top_codes + (["기타"] if has_other else [])
+        return {"chargers": result, "error_codes": all_codes}
+    finally:
+        db.close()