[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/CLAUDE.md

@@ -60,8 +60,17 @@ SOLUTION_ERP/
 │   ├── PROJECT-MAP.md
 │   ├── forms-spec.md               ⭐ 8 form catalog + RG-001 code format
 │   ├── workflow-contract.md        ⭐ 9 phase state machine + role matrix
+│   ├── database/
+│   │   └── database-guide.md       ⭐ Conventions, schema hiện tại + planned, ERD, migration workflow
+│   ├── flows/                      ⭐ Sequence/state diagram mỗi feature
+│   │   ├── README.md               (index)
+│   │   ├── auth-flow.md            ✅ implemented
+│   │   ├── permission-flow.md      📝 Phase 1 đợt 2
+│   │   ├── contract-creation-flow.md  📝 Phase 2
+│   │   ├── contract-approval-flow.md  📝 Phase 3
+│   │   ├── form-render-flow.md     📝 Phase 2
+│   │   └── sla-expiry-flow.md      📝 Phase 3
 │   ├── guides/                     setup, cicd, code-rules...
-│   ├── database/                   schema docs
 │   └── changelog/
 │       ├── migration-todos.md      Roadmap 5 phase
 │       └── sessions/               YYYY-MM-DD session logs