Right-size submit CTA + match input to card shape

- Submit button height/text now match the bottom "다른 경기 투표하기"
  CTA (py-3, text-15) — was oversized (py-5, text-19)
- Keep rounded-2xl so roundness stays consistent with the green card
- Email input matched to same rounded-2xl shape and height

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

components/Arena.tsx

@@ -282,7 +282,7 @@ export default function Arena({
             value={email}
             onChange={(e) => setEmail(e.target.value)}
             placeholder={t.emailPh}
-            className="w-full rounded-xl border border-[var(--share)] bg-[#0f1217] px-4 py-3.5 text-[16px] text-white shadow-[0_0_0_2px_rgba(166,94,255,0.12)] outline-none focus:shadow-[0_0_0_2px_rgba(166,94,255,0.3)]"
+            className="w-full rounded-2xl border border-[var(--share)] bg-[#0f1217] px-4 py-3 text-[16px] text-white shadow-[0_0_0_2px_rgba(166,94,255,0.12)] outline-none focus:shadow-[0_0_0_2px_rgba(166,94,255,0.3)]"
           />
           <label className="mt-2.5 flex items-start gap-2 text-[13px] leading-snug text-[var(--ink-muted)]">
             <input
@@ -296,7 +296,7 @@ export default function Arena({
           <button
             onClick={confirmSubmit}
             disabled={!emailValid}
-            className="btn-share mt-3.5 flex w-full items-center justify-center gap-2 rounded-2xl py-5 text-[19px] font-extrabold transition active:scale-[0.99] disabled:opacity-[0.72]"
+            className="btn-share mt-3.5 flex w-full items-center justify-center gap-1.5 rounded-2xl py-3 text-[15px] font-extrabold transition active:scale-[0.99] disabled:opacity-[0.72]"
           >
             {t.submit} <span aria-hidden>→</span>
           </button>