docs(crm): capture association graph and invoice/mail quirks

Document Medex-learned OO rules (one company, entityId at create, PDF
cache/cleanup, Matrix # truncation) and add invoices pdf/status helpers.

CHANGELOG.md

@@ -4,6 +4,18 @@ All notable changes to this project are documented here. The format is based on
 [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and this project
 adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Added
+
+* **docs:** CRM association graph and OO quirks (`docs/crm-associations.md`)
+* **crm:** `ForceRegenerateInvoicePDF`, `SetInvoiceStatus`, `PurgeStaleInvoicePDFs`, contact/opportunity file list helpers
+* **oo:** `invoices pdf`, `pdf-cleanup`, `status`; create `--consignee`; draft-invoice force-regens PDF
+
+### Fixed
+
+* Document that invoice→deal must be set at create (`update --opportunity` often HTTP 400)
+
 ## [0.9.0](https://github.com/eSlider/go-onlyoffice/compare/v0.8.3...v0.9.0) (2026-07-26)