feat(ui): 100만원 챌린지 룰 설명 모달 추가

'100만 원에 도전하기' 버튼 클릭 시 모달 표시 — 배점표(정확5/근접3/승패2/부분1/빗나감0),
누적 1위 상금, 이메일 기준 참여·집계 안내. KO/EN 지원.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/Arena.tsx

@@ -49,6 +49,7 @@ export default function Arena({
   const [copied, setCopied] = useState(false);
   const [submitting, setSubmitting] = useState(false);
   const [error, setError] = useState<string | null>(null);
+  const [showRules, setShowRules] = useState(false);
 
   // 점수 선택 시 승/무/패 자동 선택 (스코어가 결과의 소스)
   useEffect(() => {
@@ -359,12 +360,69 @@ export default function Arena({
               {t.goldDesc}
             </p>
           </div>
-          <button className="gold-btn shrink-0 whitespace-pre-line rounded-xl px-4 py-3.5 text-[14px] font-extrabold leading-tight active:scale-[0.98]">
+          <button
+            onClick={() => setShowRules(true)}
+            className="gold-btn shrink-0 whitespace-pre-line rounded-xl px-4 py-3.5 text-[14px] font-extrabold leading-tight active:scale-[0.98]"
+          >
             {t.goldBtn}
           </button>
         </div>
       </section>
 
+      {/* ===== 룰 설명 모달 ===== */}
+      {showRules && (
+        <div
+          className="fixed inset-0 z-50 flex items-center justify-center bg-black/65 p-4"
+          onClick={() => setShowRules(false)}
+        >
+          <div
+            className="w-full max-w-[420px] rounded-2xl border border-[var(--gold-border)]/45 bg-[var(--bg2)] p-5"
+            style={{ boxShadow: "0 20px 60px rgba(0,0,0,0.6)" }}
+            onClick={(e) => e.stopPropagation()}
+          >
+            <div className="flex items-center gap-1.5 text-[18px] font-extrabold text-[var(--gold-border)]">
+              <span>{t.rulesTitle}</span>
+              <span>★</span>
+            </div>
+            <p className="mt-2 text-[13px] leading-snug text-white/80">{t.rulesCumulative}</p>
+
+            <div className="mt-4 space-y-1.5">
+              {(
+                [
+                  [t.rulesExact, 5],
+                  [t.rulesCloseGrade, 3],
+                  [t.rulesOutcome, 2],
+                  [t.rulesPartial, 1],
+                  [t.rulesMiss, 0],
+                ] as [string, number][]
+              ).map(([label, pt]) => (
+                <div
+                  key={label}
+                  className="flex items-center justify-between rounded-lg border border-[var(--line-d)] px-3 py-2 text-[13px]"
+                >
+                  <span className="font-semibold text-white/85">{label}</span>
+                  <span className="font-extrabold text-[var(--green)]">
+                    {pt}
+                    {lang === "en" ? " pt" : "점"}
+                  </span>
+                </div>
+              ))}
+            </div>
+
+            <p className="mt-4 rounded-lg border border-[var(--mint)]/35 bg-[var(--mint)]/10 px-3 py-2.5 text-[12.5px] font-bold leading-snug text-[var(--mint)]">
+              {t.rulesEmailRequired}
+            </p>
+
+            <button
+              onClick={() => setShowRules(false)}
+              className="btn-mint mt-4 w-full rounded-xl py-3 text-[15px] font-extrabold active:scale-[0.99]"
+            >
+              {t.rulesCloseBtn}
+            </button>
+          </div>
+        </div>
+      )}
+
       {/* ===== Crowd Pick (003) — 보팅 비율(≠ AI 승리 확률) ===== */}
       <section className="mt-6">
         <div className="mb-2.5 text-[20px] font-extrabold">

frontend/src/lib/i18n.ts

@@ -74,6 +74,15 @@ type Dict = {
   copied: string;
   goldDesc: string;
   goldBtn: string;
+  rulesTitle: string;
+  rulesCumulative: string;
+  rulesExact: string;
+  rulesCloseGrade: string;
+  rulesOutcome: string;
+  rulesPartial: string;
+  rulesMiss: string;
+  rulesEmailRequired: string;
+  rulesCloseBtn: string;
   crowdSub: string;
   finalResult: string;
   hit: string;
@@ -133,6 +142,16 @@ export const DICT: Record<Lang, Dict> = {
     copied: "복사됨 ✓",
     goldDesc: "경기마다 승패·스코어를 맞혀 포인트를 쌓고, 누적 1위에게 최종 100만원",
     goldBtn: "100만 원에\n도전하기",
+    rulesTitle: "100만 원 챌린지 룰",
+    rulesCumulative: "경기마다 적중 포인트를 쌓아, 대회 누적 포인트 1위 한 분에게 최종 100만 원을 드립니다.",
+    rulesExact: "정확 스코어 적중",
+    rulesCloseGrade: "근접 (승패 + 득실차 일치)",
+    rulesOutcome: "승패만 적중",
+    rulesPartial: "부분 (한 팀 스코어만 일치)",
+    rulesMiss: "빗나감",
+    rulesEmailRequired:
+      "픽 제출 시 입력한 이메일로 챌린지에 참여됩니다. 같은 이메일의 모든 경기 포인트가 합산되어 누적 순위가 매겨집니다.",
+    rulesCloseBtn: "확인",
     crowdSub: "| 참여자들의 선택",
     finalResult: "최종 결과",
     hit: "적중 ✓",
@@ -191,6 +210,16 @@ export const DICT: Record<Lang, Dict> = {
     copied: "Copied ✓",
     goldDesc: "Earn points each match by nailing the result & score — the overall #1 wins ₩1,000,000.",
     goldBtn: "Go for\n₩1,000,000",
+    rulesTitle: "₩1,000,000 Challenge Rules",
+    rulesCumulative: "Earn points each match — the player with the highest cumulative total wins ₩1,000,000.",
+    rulesExact: "Exact score",
+    rulesCloseGrade: "Close (result + goal difference)",
+    rulesOutcome: "Correct result only",
+    rulesPartial: "Partial (one team's score)",
+    rulesMiss: "Miss",
+    rulesEmailRequired:
+      "You enter the challenge with the email you provide when submitting a pick. Points from all matches under the same email are summed for the overall ranking.",
+    rulesCloseBtn: "Got it",
     crowdSub: "| What the crowd picked",
     finalResult: "Final result",
     hit: "Hit ✓",