feat(chart): CSV export of current chart range + fix ShareButton comment

- New lib/csv.ts: RFC 4180 escaping, UTF-8 BOM prefix (한글 Excel 호환),
  Blob + temporary anchor download, filename
  `<name>_<code>_<interval>_<from>_<to>.csv` with filesystem-illegal
  characters replaced by `_`.
- StockChart toolbar now always renders (was hidden in 10m intraday mode
  because it gated on showSma) and includes a right-aligned `⬇ CSV`
  button next to the SMA/RSI/MACD chips. Button is disabled when ohlcv
  is empty.

Also addresses the reviewer's non-blocking note on f18493f:
ShareButton.tsx header comment claimed clipboard-first, but the code
calls navigator.share() first. Comment now matches the actual order:
share → clipboard → execCommand → "복사 안됨".

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/components/ShareButton.tsx

@@ -1,12 +1,13 @@
 "use client";
 
-// 종목 페이지 공유 버튼 — 현재 URL 을 클립보드에 복사.
-// Toss 의 종목 공유 패턴 (개별 모달 없이 즉시 복사 + 짧은 토스트).
+// 종목 페이지 공유 버튼 — 현재 URL 을 공유 / 클립보드에 복사.
+// Toss 의 종목 공유 패턴 (개별 모달 없이 즉시 시도 + 짧은 토스트).
 //
-// 폴백 순서:
-//   1) navigator.clipboard.writeText (HTTPS or localhost)
-//   2) document.execCommand("copy") (legacy, http LAN 등 secure context 아닌 경우)
-//   3) 두 경로 모두 실패면 "복사 안됨" 안내
+// 동작 우선순위:
+//   1) navigator.share (모바일 native sheet — 성공 시 OS 시트가 피드백, 토스트 안 띄움)
+//   2) navigator.clipboard.writeText (HTTPS or localhost — 클립보드에 복사 + "링크 복사됨")
+//   3) document.execCommand("copy") (legacy, http LAN 등 secure context 아닌 경우)
+//   4) 모두 실패면 "복사 안됨" 안내
 
 import { useEffect, useState } from "react";
 

web/components/StockChart.tsx

@@ -14,6 +14,7 @@ import {
   type UTCTimestamp,
 } from "lightweight-charts";
 import type { ChartPayload, LatestPredictionResponse } from "../lib/api";
+import { csvFilename, downloadCsv, ohlcvToCsv } from "../lib/csv";
 import type { Targets } from "../lib/targets";
 
 type Props = {
@@ -755,8 +756,9 @@ export function StockChart({ chart, prediction, targets }: Props) {
 
   return (
     <div className="w-full rounded-lg border border-zinc-800 bg-zinc-900/30 p-2">
-      {showSma && (
       <div className="mb-1 flex flex-wrap items-center gap-1.5 px-1">
+        {showSma && (
+          <>
             {SMA_PRESETS.map((p) => {
               const on = active.has(p.window);
               return (
@@ -814,8 +816,27 @@ export function StockChart({ chart, prediction, targets }: Props) {
               />
               MACD
             </button>
-        </div>
+          </>
         )}
+        <button
+          type="button"
+          onClick={() => {
+            const filename = csvFilename(
+              chart.name,
+              chart.code,
+              chart.interval,
+              chart.range.from,
+              chart.range.to,
+            );
+            downloadCsv(filename, ohlcvToCsv(chart.ohlcv));
+          }}
+          disabled={!chart.ohlcv.length}
+          className="ml-auto flex items-center gap-1 rounded-full border border-zinc-800 px-2 py-0.5 text-[10px] text-zinc-400 transition hover:border-zinc-600 hover:text-zinc-200 disabled:cursor-not-allowed disabled:opacity-40"
+          title="현재 봉 데이터를 CSV 로 내보내기 (UTF-8 BOM, Excel 호환)"
+        >
+          ⬇ CSV
+        </button>
+      </div>
       <div className="relative h-[460px] w-full">
         <div ref={containerRef} className="h-full w-full" />
         <CrosshairLabel info={hover ?? lastSummary} isHover={hover != null} />

web/lib/csv.ts

@@ -0,0 +1,69 @@
+// OHLCV → CSV 변환 + 다운로드 트리거.
+// 차트 데이터를 분석가 친화 CSV (UTF-8 BOM, Excel 호환) 로 내려받게 해줌.
+
+import type { ChartInterval, OhlcvPoint } from "./api";
+
+function escapeField(v: string): string {
+  // 표준 RFC 4180 — 쉼표/큰따옴표/개행 포함 시 큰따옴표로 감싸고 내부 큰따옴표는 이중화.
+  if (v.includes(",") || v.includes('"') || v.includes("\n")) {
+    return `"${v.replace(/"/g, '""')}"`;
+  }
+  return v;
+}
+
+function num(n: number | null | undefined): string {
+  if (n == null || !Number.isFinite(n)) return "";
+  return String(n);
+}
+
+export function ohlcvToCsv(ohlcv: OhlcvPoint[]): string {
+  const header = ["date", "open", "high", "low", "close", "volume"];
+  const lines: string[] = [header.join(",")];
+  for (const p of ohlcv) {
+    lines.push(
+      [
+        escapeField(p.date),
+        num(p.open),
+        num(p.high),
+        num(p.low),
+        num(p.close),
+        num(p.volume),
+      ].join(","),
+    );
+  }
+  return lines.join("\n");
+}
+
+export function downloadCsv(filename: string, csv: string): boolean {
+  if (typeof window === "undefined" || typeof document === "undefined") return false;
+  // Excel BOM — 한글 Excel 이 UTF-8 로 추론하도록.
+  const BOM = "\uFEFF";
+  const blob = new Blob([BOM + csv], { type: "text/csv;charset=utf-8" });
+  const url = URL.createObjectURL(blob);
+  try {
+    const a = document.createElement("a");
+    a.href = url;
+    a.download = filename;
+    a.style.display = "none";
+    document.body.appendChild(a);
+    a.click();
+    document.body.removeChild(a);
+    return true;
+  } catch {
+    return false;
+  } finally {
+    setTimeout(() => URL.revokeObjectURL(url), 0);
+  }
+}
+
+// `삼성전자_005930_1d_2025-08-01_2025-11-28.csv` — 파일시스템 금지 문자만 `_` 치환.
+export function csvFilename(
+  name: string,
+  code: string,
+  interval: ChartInterval,
+  from: string,
+  to: string,
+): string {
+  const safe = (s: string) => s.replace(/[\\/:*?"<>|]/g, "_").trim() || "data";
+  return `${safe(name)}_${code}_${interval}_${from}_${to}.csv`;
+}