Improve orderbook depth profile contrast

[jackhai9]

Summary

• reduce the depth profile background mix from 72% to 24%
• remove group opacity from the canvas and raise bid/ask bar alpha to 62%
• keep one-pixel price rows, geometry, pointer behavior, and the current-price divider unchanged
• bump the orderbook userscript to 2.7.200 and rebuild the install artifact

Validation

• npm test (766 passed)
• npm run test:ui (64 passed)
• npm run build:binance-orderbook-trade
• npm run check:binance-orderbook-trade
• npm run check:binance-userscripts
• npm run inspect:binance-orderbook-trade
• git diff --check
• independent read-only review: approved with no findings

Live validation

Tampermonkey exact-source synchronization, hard reload, loaded-source verification, and the non-financial depth-profile visual check will run after merge.