refactor: switch database architecture from PostgreSQL to SQLite

PLAN.md

@@ -6,7 +6,7 @@ This document outlines the technical architecture for the unified Inventory Syst
 
 ### 1. Backend Server (Linux / Docker)
 - **Framework:** Python + FastAPI
-- **Database:** PostgreSQL
+- **Database:** SQLite (SQLAlchemy ORM)
 - **Key Modules:**
   - `Items / Interventions`: Standard CRUD logic.
   - `Audit`: Every payload that mutates data writes an immutable log row.
@@ -24,7 +24,7 @@ This document outlines the technical architecture for the unified Inventory Syst
 
 ## Implementation Phases
 
-- **Phase 1: Database & Backend Foundation** - Docker setup, PostgreSQL schemas, User management, and Python API structures.
+- **Phase 1: Database & Backend Foundation** - SQLite schemas, User management, and Python API structures.
 - **Phase 2: Core Inventory API** - Endpoints to Add/Remove items, offline sync-merge logic, Audit triggers.
 - **Phase 3: The PWA Frontend** - PWA manifest, offline capabilities, UI scaffolding for Desktop/Mobile.
 - **Phase 4: Client-Side Scanning** - Integration of local JS barcode reading for routine stock scanning.

requirements.md

@@ -7,7 +7,7 @@ A unified system to maintain an inventory of "items" and their quantities, inclu
 
 ### 2.1 Main Application Server (Linux Backend)
 *   **Target Environment:** Dockerized Linux Environment.
-*   **Framework:** Python (FastAPI) + PostgreSQL database.
+*   **Framework:** Python (FastAPI) + SQLite database.
 *   **Users & Security:** Support multiple authenticated users with distinct actions.
 *   **Audit Compliance:** **All operations** must maintain a strict audit log detailing who changed what and when.