feat: withdraw excess USDT automatically when Futures becomes flat

[jackhai9]

Automatically withdraw excess Futures USDT once an ordinary USDⓈ-M account has no positions or open orders for two seconds. The automatic path retains the existing 10% allocation target but never debits Funding/Spot or refills Futures after losses. Manual full rebalancing still requires confirmation.

Account-specific persistent state prevents duplicate transfers across tabs and reloads. Each transfer rechecks identity, all-symbol positions, basic and conditional orders, and balances; an unknown outcome stops further transfers. Script trading and transfers share a browser lock. Task controllers are established before waiting for that lock so an immediate Stop remains effective. Automatic status appears separately from retained trading results.

Validation:

• 2,257 Node tests passed on the final source; test lint, generated build, syntax, and diff checks passed.
• Targeted browser scenarios cover no-refill, two tabs, reloads, unknown responses, lock contention, immediate Stop, cancellation boundaries, native validation, manual confirmation, and independent status messages.
• Independent architecture and final code reviews passed. The final automatic-completion panel was rendered and inspected locally.
• Read-only live checks verified the native identity and complete Basic/Conditional order response contracts. No real transfer was executed for testing.
• Remote CI validates the final PR commit, including the complete browser suite. These checks do not claim complete source coverage.

Version: orderbook v2.7.221. Automatic execution is limited to ordinary symbol routes without query parameters and verified non-portfolio accounts. Native Binance actions, older loaded script versions, other browsers, and external devices remain outside the script lock.