docs: reorganize by reader, add integrator reference and ledger pages, fix drift New: Operations Contract, Errors and Rate Limits, Versioning and Compatibility, Build a Ledger Integration, SEC Data Model and Query Rules, QuickBooks Sync and Write Policy, Chart of Accounts Mapping, Period Close, Forecasting and Metrics, Information Block Reference, Event Block Reference. Information Blocks and Event-Driven Ledger split into concept and reference. SEC Cypher examples follow the four query rules. Sidebar and Home grouped by what the reader is doing. Stale claims corrected against the code.