[CLAUDE] Docs: database-guide + 6 flow diagrams

docs/database/database-guide.md:
- Conventions (naming, data types, audit fields, soft delete)
- Schema hien tai (Identity tables sau migration Init) + seed 12 role + admin
- Schema planned: Phase 1 dot 2 (Supplier/Project/Department + Permission Matrix)
- Schema planned: Phase 3 (Contract + Approval + Comment + Attachment + Template + Clause + CodeSequence)
- Mermaid ERD cho tung phase
- Migration workflow (create/apply/revert)
- Index strategy + unique indexes
- Backup/restore SQL
- Common pitfalls + SQL cheatsheet

docs/flows/ — 6 flow documentation:
- README.md: index
- auth-flow.md: login/refresh/me/logout (IMPLEMENTED, sequence + edge cases + security checklist)
- permission-flow.md: Phase 1 dot 2 - Role x MenuKey x CRUD resolution + FE guard + BE policy
- contract-creation-flow.md: Phase 2 - Drafter flow chon template -> fill -> preview -> save draft
- contract-approval-flow.md: Phase 3 - state machine 9 phase chi tiet + reject flow + timeline UI
- form-render-flow.md: Phase 2 - OpenXml + ClosedXML + LibreOffice PDF convert
- sla-expiry-flow.md: Phase 3 - BackgroundService auto-approve qua SLA + warning notify

Update references:
- CLAUDE.md (root): them 2 row Tai lieu quan trong
- docs/CLAUDE.md: update project layout voi flows/ + database/
- docs/STATUS.md: log docs addition
- docs/changelog/migration-todos.md: tick Phase 0 docs items

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -68,6 +68,8 @@ Kiến trúc: **.NET 10 Clean Architecture + 2 React FE (admin + user) + SQL Ser
 | [`docs/CLAUDE.md`](docs/CLAUDE.md) | Full context — tech stack, architecture |
 | [`docs/workflow-contract.md`](docs/workflow-contract.md) | State machine 9 phase + role matrix |
 | [`docs/forms-spec.md`](docs/forms-spec.md) | Catalog 8 form + quy định mã HĐ |
+| [`docs/database/database-guide.md`](docs/database/database-guide.md) | DB conventions + schema hiện tại + planned + ERD |
+| [`docs/flows/README.md`](docs/flows/README.md) | Index 6 flow (auth, permission, contract create/approve, form render, SLA) |
 
 ## ⚠️ Kết thúc session