Fix Binance tasks paused in hidden tabs

[jackhai9]

Summary

• Continue already-started Binance ladder, continuous-close, single-order, confirmed cancellation, and confirmed rebalance workflows when the tab becomes hidden.
• Observe native form inputs and action buttons through independent background timer tasks while paint frames are paused; preserve Stop cancellation and pre-submit context checks.
• Reject a single-order draft older than 15 seconds before native submission, including after a long hidden-page stall.
• Bump the generated orderbook userscript to 2.7.212 and document Chrome lifecycle limits and live validation steps.

Validation

• npm test — 2083 passed in the isolated release worktree.
• npm run lint:tests, npm run build:binance-orderbook-trade, npm run check:binance-orderbook-trade, npm run inspect:binance-orderbook-trade, and git diff --check passed.
• Four affected Playwright specs passed 90/90 after the background-task change. The order-submit spec passed 30/30 after adding the stale-draft guard. The final dual-clock guard passed its two focused background scenarios.

Live validation boundary

L2 tests simulate document.hidden and paused animation frames against the generated userscript. They do not simulate Chrome timer throttling, freeze/discard, Tampermonkey injection, or a live Binance account. No real order, cancellation, or transfer was performed.