docs: Update CLAUDE.md - remove Docker dependency from local dev, use native PostgreSQL

CLAUDE.md

@@ -13,15 +13,22 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 ### Prerequisites
 - .NET 10 SDK
 - Node.js 22 / pnpm 10
-- PostgreSQL 17 (local via Docker Compose)
-- Docker & Docker Compose
+- PostgreSQL 17 (installed locally)
+
+### Local PostgreSQL Setup
+
+Ensure PostgreSQL 17 is running locally on default port 5432. Create the database and user:
+
+```sql
+CREATE DATABASE kartsell;
+CREATE USER kartsell WITH PASSWORD 'kartsell';
+ALTER ROLE kartsell CREATEDB;
+GRANT ALL PRIVILEGES ON DATABASE kartsell TO kartsell;
+```
 
 ### Local Development Environment
 
 ```bash
-# Start PostgreSQL
-docker-compose up -d
-
 # Backend: restore, build, migrate, test
 dotnet restore KArtSell.sln
 dotnet build KArtSell.sln -c Release
@@ -59,6 +66,16 @@ Password: kartsell
 
 Environment variable: `KARTSELL_POSTGRES=Host=localhost;Port=5432;Database=kartsell;Username=kartsell;Password=kartsell`
 
+**On Windows (PowerShell):**
+```powershell
+$env:KARTSELL_POSTGRES="Host=localhost;Port=5432;Database=kartsell;Username=kartsell;Password=kartsell"
+```
+
+**On macOS/Linux (bash):**
+```bash
+export KARTSELL_POSTGRES="Host=localhost;Port=5432;Database=kartsell;Username=kartsell;Password=kartsell"
+```
+
 ## Architecture
 
 ### Backend: Modular Monolith + Vertical Slices