fix: 베팅과 게임 정보 창을 화면 중앙에 배치한다

공통 viewport 중앙 배치 규칙을 추가하고 데스크톱·모바일 Chromium 좌표 회귀 검사를 보강한다.

app/game-frontend/src/assets/main.css

@@ -64,6 +64,17 @@ textarea {
     font: inherit;
 }
 
+/*
+ * Tailwind's reset removes the native dialog's auto margins. Dialogs that are
+ * meant to float over the current screen opt back into explicit viewport
+ * centring instead of inheriting the document's 500px legacy canvas.
+ */
+.viewport-centered-dialog {
+    position: fixed;
+    inset: 0;
+    margin: auto;
+}
+
 /*
  * Firefox for Android may zoom to a focused search field. `manipulation`
  * suppresses that focus-only zoom while retaining ordinary pan and pinch zoom.

app/game-frontend/src/views/BettingView.vue

@@ -150,7 +150,12 @@ const placeBet = async () => {
             @request-bet="openBetDialog"
         />
 
-        <dialog ref="betDialog" class="bet-dialog" aria-labelledby="bet-dialog-title" @close="selectedTarget = null">
+        <dialog
+            ref="betDialog"
+            class="bet-dialog viewport-centered-dialog"
+            aria-labelledby="bet-dialog-title"
+            @close="selectedTarget = null"
+        >
             <form v-if="selectedTarget" class="bet-dialog-content" @submit.prevent="placeBet">
                 <header>
                     <h2 id="bet-dialog-title">베팅하기</h2>

app/game-frontend/src/views/MainView.vue

@@ -585,7 +585,11 @@ watch(
         @quick="moveQuick"
         @action="handleNavigationAction"
     />
-    <dialog ref="versionDialog" class="game-version-dialog" aria-labelledby="game-version-title">
+    <dialog
+        ref="versionDialog"
+        class="game-version-dialog viewport-centered-dialog"
+        aria-labelledby="game-version-title"
+    >
         <h2 id="game-version-title">게임 정보</h2>
         <p>{{ lobbyInfo?.scenarioTitle || 'Core2026' }}</p>
         <p>삼국지 모의전투 Core2026</p>