feat: add Japanese language support, three-language subtitles for all demo scenes

src/locales/ja.json

@@ -0,0 +1,79 @@
+{
+  "ui": {
+    "start": "はじめる",
+    "resume": "つづきから",
+    "chapters": "チャプター",
+    "menu": "メニュー",
+    "save": "セーブ",
+    "load": "ロード",
+    "close": "とじる",
+    "skip": "スキップ",
+    "fullscreen": "フルスクリーン",
+    "exitFullscreen": "フルスクリーン解除",
+    "gameEnd": "おわり",
+    "choose": "選んでください",
+    "back": "もどる",
+    "autoSave": "オートセーブ",
+    "empty": "なし",
+    "loading": "読み込み中...",
+    "speed": "倍速",
+    "noAutoSave": "オートセーブがありません",
+    "autoSaveHint": "シーン切替時にスロット0に自動保存されます"
+  },
+  "scene": {
+    "intro": {
+      "choice": {
+        "left_door": "左にある光るドアへ向かう",
+        "right_door": "右にある普通のドアへ向かう",
+        "search": "部屋を念入りに調べる",
+        "stay": "その場に留まる"
+      }
+    },
+    "left_door": {
+      "choice": {
+        "handshake": "見知らぬ人と握手する",
+        "reject": "握手を断り、警戒を続ける"
+      }
+    },
+    "right_door": {
+      "choice": {
+        "continue": "先へ進む",
+        "back": "引き返す"
+      }
+    },
+    "trust_ending": {
+      "choice": {
+        "journey": "信頼の旅に出る（trust >= 80 が必要）",
+        "leave": "ここを去る"
+      }
+    },
+    "investigation_site": {
+      "choice": {
+        "leave": "部屋を出る"
+      }
+    },
+    "desk_detail": {
+      "choice": {
+        "return": "調査現場に戻る",
+        "leave": "立ち去る"
+      }
+    },
+    "stay": {
+      "choice": {
+        "stand": "立ち上がって去る"
+      }
+    },
+    "qte_success": {
+      "choice": {
+        "continue": "先へ進む",
+        "back": "引き返す"
+      }
+    },
+    "qte_fail": {
+      "choice": {
+        "continue": "先へ進む",
+        "back": "引き返す"
+      }
+    }
+  }
+}