docs: refactor documentation for portability and SSOT v1.2.7

PLAN.md

@@ -3,19 +3,8 @@
 This document defines the technical architecture and rules for the InventoryAI System (2026 Edition).
 
 ## 1. Core Architecture
-
-### 1.1 Backend (Python 3.14+)
-- **Framework:** FastAPI
-- **Database:** SQLite (SQLAlchemy) - chosen for local performance and simplicity.
-- **Organization:** Modular design with separate routers for Items and Operations.
-
-### 1.2 Frontend (Next.js 15+ PWA)
-- **State Management:** React Hooks + Dexie.js (IndexedDB wrapper).
-- **Offline Engine:** 
-  - Service Workers for asset caching.
-  - IndexedDB for local data persistence.
-  - Sync mechanism: Local changes are buffered and pushed to backend when online.
-- **Scanner:** `html5-qrcode` for standard barcode/QR detection (Local-only).
+See the detailed [dev_docs/TECH_STACK.md](dev_docs/TECH_STACK.md) for official framework, database, and library versions.
+Summary: FastAPI / Python 3.12+ (Backend) & Next.js 15+ PWA (Frontend). Sync via Dexie.js (client side) and SQL sync logic (v1.2.4).
 
 ## 2. AI Intelligence Strategy (Critical)