docs: refactor documentation for portability and SSOT v1.2.7

dev_docs/TECH_STACK.md

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+# TECHNICAL STACK - SINGLE SOURCE OF TRUTH
+
+This document defines the official technology stack for the Inventory System. All components must adhere to these versions and libraries.
+
+## 🟢 Backend (API & Data)
+- **Language:** Python 3.12+ (Optimized for performance and type safety)
+- **Framework:** [FastAPI](https://fastapi.tiangolo.com/) (Async ASGI)
+- **Database:** SQLite (SQLAlchemy) - Local file-based persistence
+- **Validation:** Pydantic v2
+- **Auth:** Hybrid LDAP (python-ldap) + PBKDF2 local password hash caching (v1.2.4)
+- **AI Engine:** Google GenAI SDK (Gemini 2.0 Flash) - Location: `backend/ai/`
+
+## 🔵 Frontend (Web & PWA)
+- **Architecture:** [Next.js](https://nextjs.org/) 15+ (App Router)
+- **Styling:** Tailwind CSS (Readability-first config: No uppercase/tracking-widest)
+- **Icons:** [Lucide Icons](https://lucide.dev/) (React components)
+- **Offline persistence:** [Dexie.js](https://dexie.org/) (IndexedDB wrapper)
+- **Scanner:** `html5-qrcode` (Client-side, offline-only)
+- **Sync:** Axios with bulk-sync idempotency (UUID-based)
+
+## 🏗 Operations & Tooling
+- **PWA Deployment:** `next-pwa` (Service Workers + Manifest.json)
+- **HTTPS Proxy:** `local-ssl-proxy` (Required for mobile camera access)
+- **Version Control:** Git (Local-first, path in `.git_path`)
+- **Isolation:** Python `.venv` and Node `node_modules`