Match Binance ladder normalized empty rollback

[jackhai9]

Root cause

The ladder input reader normalizes controlled input values with normalizeDecimalString, which maps an empty input to null. The ladder recovery policy incorrectly allowed only the raw empty string, so it rejected the exact normalized rollback even when the input identity, form root, write budget, and provisional recovery contract were all valid. Raw CDP breakpoint evidence confirmed rollbackValue=null with recovery otherwise eligible.

Changes

• match the ladder recovery policy to the exact normalized empty value (null)
• use the production decimal normalizer/comparator in recovery tests
• lock the normalized policy in source-regression tests
• bump the userscript version to 2.7.138

Validation

• npm test (371/371)
• focused trade-form/source regression tests (78/78)
• npm run build:binance-orderbook-trade
• npm run check:binance-orderbook-trade
• git diff --check
• raw CDP closure-variable diagnosis
• independent read-only root-cause and final-diff reviews