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/en.json

@@ -3333,6 +3333,7 @@
 		"dragToMove": "Drag to move",
 		"hide": "Hide toolbar",
 		"fullscreenExit": "Exit fullscreen",
-		"show": "Show toolbar"
+		"show": "Show toolbar",
+		"emulatorUnknown": "Emulator status unknown"
 	}
 }