[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>

docs/changelog/migration-todos.md

@@ -15,6 +15,8 @@
 - [x] Parse 8 form → `docs/forms-spec.md`
 - [x] Parse quy trình → `docs/workflow-contract.md`
 - [x] Viết `docs/{CLAUDE,STATUS,PROJECT-MAP}.md`
+- [x] Viết `docs/database/database-guide.md` (conventions + schema + ERD + migration workflow)
+- [x] Viết `docs/flows/` — README + 6 flow doc (auth, permission, contract-create, contract-approve, form-render, sla-expiry)
 - [x] Viết `.gitignore`, `README.md`, `global.json`, `docker-compose.yml`
 - [x] Tạo placeholder skill folders: `contract-workflow`, `form-engine`, `permission-matrix`
 - [x] `git init` + commit đầu (`25dad7f`)