feat: polish toolbar, live online count via SSE + emulator 3-state

- Add emulator status 3-state (unknown/green/red) with tooltip
- Extract shared primary button style/constants for DRY toolbar code
- Add emulatorUnknown translations to all 25 locales
- Bump Next.js to 16.3.4
- Fix RCON delivery timeout caching (15s TTL / shared across clients)
- Who's-online tooltip throttled to max 1 request per 30s

src/messages/ja.json

@@ -21,6 +21,7 @@
 		"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"
+		"show": "ツールバーを表示",
+		"emulatorUnknown": "エミュレータの状態が不明です"
 	}
 }