perf: accelerate ladder order replacement

[jackhai9]

Summary

• observe row removal and confirmation dialogs concurrently during ladder order replacement
• keep a short stable-removal confirmation without the per-row 1.8 second empty dialog wait
• keep ladder action slots fixed and turn only the active action into the stop control

Validation

• npm test (351/351)
• npm run build:binance-orderbook-trade
• npm run check:binance-orderbook-trade
• git diff --check
• independent read-only review passed