feat: refine ladder layout and precision refresh

[jackhai9]

Summary

• match the custom panel divider to the live Binance divider style
• narrow the shared two-character label column so ladder and precision controls gain usable width
• rename the visible precision label to 精度
• replace the six-second polling sampler with one immediate latest-trade DOM snapshot
• start with the latest 10 trades and expand by 10 only when there are fewer than five effective price moves
• show 近期价格变化不足，请稍后重试 only after the complete visible trade list is exhausted
• remove obsolete sampling timers, queue state, and accumulated-sample behavior

Validation

• npm test (327/327)
• npm run build:binance-orderbook-trade
• npm run check:binance-orderbook-trade
• git diff --check
• precision refresh Playwright paths (2/2)
• panel visual contracts (2/2)
• full UI suite: 48/49 on first run; the unrelated pairwise-05 no-order timing case then passed 3/3 in isolation