feat(client): polished toolbar, live online count via SSE

- Redesign in-game client toolbar with refined glass styling and buttons
- Live online count + emulator status streamed over SSE multicast
- Who's-online tooltip throttled to reduce repeated requests
- Fix show button so it always returns the hidden toolbar
- Use theme CSS variables instead of hardcoded colors
- Add toolbar translations across all 25 locales

src/messages/ja.json

@@ -9,5 +9,18 @@
 				"studio": "Studio"
 			}
 		}
+	},
+	"toolbar": {
+		"home": "ホーム",
+		"reload": "再読み込み",
+		"fullscreen": "全画面",
+		"logout": "ログアウト",
+		"onlineUsers": "オンラインのユーザー",
+		"emulatorOnline": "エミュレータオンライン",
+		"emulatorOffline": "エミュレータオフライン",
+		"dragToMove": "ドラッグして移動",
+		"hide": "ツールバーを隠す",
+		"fullscreenExit": "全画面を終了",
+		"show": "ツールバーを表示"
 	}
 }