feat: add realtime challenge client and local smoke test

backend/static/css/app.css

@@ -132,6 +132,14 @@ button { color: inherit; }
 .track-switch { display: flex; gap: 5px; margin-bottom: 22px; }
 .track-switch button { border: 1px solid var(--line); padding: 9px 18px; border-radius: 99px; background: transparent; cursor: pointer; }
 .track-switch button.active { background: var(--ink); color: white; }
+.challenge-panel { display: grid; grid-template-columns: minmax(0, 1fr) minmax(380px, .9fr); gap: 24px; align-items: center; margin-bottom: 22px; padding: 24px 26px; border: 1px solid var(--line); border-radius: 18px; background: linear-gradient(120deg, rgba(25,101,72,.07), rgba(204,232,91,.12)); }.challenge-panel h2 { margin: 7px 0 6px; font: 27px Georgia, serif; }.challenge-panel p { margin: 0; color: var(--muted); font-size: 12px; line-height: 1.7; }.challenge-actions { display: grid; gap: 9px; }.challenge-actions > .primary-button { width: 100%; }.challenge-actions form { display: grid; grid-template-columns: 1fr auto; gap: 8px; }.challenge-actions input { min-width: 0; border: 1px solid var(--line); border-radius: 10px; padding: 12px 14px; background: white; text-transform: uppercase; letter-spacing: .18em; font-weight: 700; }.challenge-actions .dark-button { width: auto; margin: 0; white-space: nowrap; }
+.realtime-status-line { display: flex; justify-content: space-between; gap: 15px; margin: 10px 0 18px; color: var(--muted); font-size: 11px; }.realtime-status-line strong { color: var(--green); }
+.realtime-waiting { display: grid; justify-items: center; gap: 16px; padding: 35px 20px; border-radius: 18px; background: #eef1eb; text-align: center; }.realtime-waiting p { max-width: 480px; margin: 0; color: var(--muted); line-height: 1.7; }.realtime-pulse { width: 18px; height: 18px; border-radius: 50%; background: var(--green); box-shadow: 0 0 0 0 rgba(25,101,72,.35); animation: realtime-pulse 1.5s infinite; }.challenge-code { border: 1px dashed var(--green); border-radius: 14px; padding: 14px 24px; background: white; color: var(--green); font: 700 31px/1 "SFMono-Regular", Consolas, monospace; letter-spacing: .22em; cursor: pointer; }
+@keyframes realtime-pulse { 70% { box-shadow: 0 0 0 15px rgba(25,101,72,0); } 100% { box-shadow: 0 0 0 0 rgba(25,101,72,0); } }
+.realtime-progress-panel { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; margin-bottom: 18px; }.realtime-progress-panel > div { padding: 13px 15px; border-radius: 12px; background: #eef1eb; }.realtime-progress-panel span, .realtime-progress-panel b { display: block; }.realtime-progress-panel span { color: var(--muted); font-size: 10px; }.realtime-progress-panel b { margin-top: 5px; color: var(--green); }
+.realtime-answer-form input { margin-top: 7px; width: 100%; padding: 12px; border: 1px solid #d6d8d1; border-radius: 9px; }.realtime-submitted { margin-top: 20px; padding: 30px; border-radius: 16px; background: var(--ink); color: white; text-align: center; }.realtime-submitted strong { color: var(--lime); font: 27px Georgia, serif; }.realtime-submitted p { margin-bottom: 0; color: #b9c2bc; }
+.realtime-result { margin: 20px 0; padding: 28px; border-radius: 17px; background: var(--ink); color: white; text-align: center; }.realtime-result > strong { color: var(--lime); font: 38px Georgia, serif; }.realtime-result p { color: #c5cec8; }.realtime-result > b { display: inline-block; padding: 6px 10px; border-radius: 99px; background: rgba(204,232,91,.13); color: var(--lime); }.result-opponent > strong { color: #ef947c; }
+.realtime-review { display: grid; gap: 9px; }.realtime-review article { padding: 15px; border: 1px solid var(--line); border-left: 4px solid var(--green); border-radius: 11px; background: white; }.realtime-review article.incorrect { border-left-color: #c05245; }.realtime-review p { margin: 7px 0; color: #3e4942; }.realtime-review small { color: var(--muted); }
 .math-games-section { margin-top: 60px; }
 .game-card-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 16px; }
 .game-card { min-height: 285px; padding: 26px; border: 1px solid var(--line); border-radius: 20px; background: var(--panel); display: flex; flex-direction: column; overflow: hidden; position: relative; }
@@ -262,6 +270,7 @@ dialog::backdrop { background: rgba(17,25,20,.55); backdrop-filter: blur(5px); }
   .content-grid { gap: 11px; }.editor-shell { min-height: 700px; }.page-title { padding-top: 42px; }.page-title h1 { font-size: 45px; }
   .tool-card { min-height: 125px; }.workspace-heading, .map-heading { display: block; }.workspace-heading p { margin-top: 12px; }.tool-workspace { padding: 16px; }.calculator-controls { grid-template-columns: 1fr 1fr; }.calculator-display { min-height: 120px; padding: 18px; }.calculator-display output { font-size: 34px; }.calc-examples .primary-button { width: 100%; margin-left: 0; }.drawing-toolbar { align-items: stretch; }.drawing-toolbar .primary-button { width: 100%; margin-left: 0; }.canvas-stage canvas { width: 100%; min-width: 0; }
   .math-games-section { margin-top: 45px; }.game-card { min-height: 260px; padding: 21px; }.game-card-controls { align-items: stretch; }.game-card-controls .primary-button { flex: 1; }.twenty-four-numbers { gap: 7px; }.twenty-four-numbers button { border-radius: 13px; font-size: 28px; }.sudoku-board input { font-size: clamp(13px, 4.5vw, 20px); }.sudoku-actions { display: grid; grid-template-columns: 1fr 1fr; }.game-keypad { gap: 5px; }
+  .challenge-panel { grid-template-columns: 1fr; padding: 20px; }.challenge-actions form { grid-template-columns: 1fr; }.challenge-actions .dark-button { width: 100%; }.challenge-code { width: 100%; padding: 14px 10px; font-size: 27px; }.realtime-status-line { display: grid; }.realtime-progress-panel { grid-template-columns: 1fr 1fr; }
   .map-stage { height: 480px; transform: scale(.92); }.ability-node { width: 108px; height: 94px; }.node-vision { left: calc(50% - 54px); }.node-humanities { left: 0; top: 100px; }.node-connection { right: 0; top: 100px; }.node-detection { left: 2%; bottom: 30px; }.node-modeling { right: 2%; bottom: 30px; }.pet-node { top: 190px; }
   .map-lines { display: none; }.ability-legend { margin-top: 14px; justify-content: start; }.video-cover { height: 150px; }
 }