[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/flows/README.md

@@ -0,0 +1,30 @@
+# Flows — SOLUTION_ERP
+
+> Document các luồng (process / sequence) chính của hệ thống. Mỗi flow có mermaid sequence diagram + API calls + side effects + edge case.
+
+## Index
+
+| Flow | Phase | Trạng thái | Doc |
+|---|---|---|---|
+| **Authentication** — login, refresh, logout, /me | 1 | ✅ Implemented | [`auth-flow.md`](auth-flow.md) |
+| **Permission resolution** — resolve menu + CRUD cho user | 1 đợt 2 | 📝 Planned | [`permission-flow.md`](permission-flow.md) |
+| **Contract creation** — tạo HĐ draft + fill form template | 2 | 📝 Planned | [`contract-creation-flow.md`](contract-creation-flow.md) |
+| **Contract approval** — state machine 9 phase | 3 | 📝 Planned | [`contract-approval-flow.md`](contract-approval-flow.md) |
+| **Form render** — template engine xuất docx/xlsx | 2 | 📝 Planned | [`form-render-flow.md`](form-render-flow.md) |
+| **SLA expiry auto-approve** — hosted service | 3 | 📝 Planned | [`sla-expiry-flow.md`](sla-expiry-flow.md) |
+
+## Quy ước đọc
+
+- **Actor:** vai trò khi thực hiện (user role hoặc system)
+- **Entry point:** ai/gì trigger
+- **API calls:** controller + endpoint (hoặc internal service)
+- **Side effects:** DB writes, file writes, notifications
+- **Edge cases:** các path lỗi / alternate
+
+Tất cả mermaid sequence/state/flowchart có thể render ở VS Code (extension Markdown Preview Mermaid), GitHub, Gitea, Gitea MD preview.
+
+## Liên quan
+
+- [`../workflow-contract.md`](../workflow-contract.md) — spec 9 phase + role matrix (domain-centric)
+- [`../forms-spec.md`](../forms-spec.md) — 8 form + mã HĐ format
+- [`../database/database-guide.md`](../database/database-guide.md) — schema chi tiết