Add Pitopn digital shop with FastAPI, Postgres 17, and Docker Compose

Co-authored-by: Cursor <cursoragent@cursor.com>

.env.example

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+# Application
+APP_NAME=Pitopn
+SECRET_KEY=change-me-to-a-long-random-string
+DEBUG=false
+
+# Database (PostgreSQL 17)
+POSTGRES_USER=pitopn
+POSTGRES_PASSWORD=change-me-strong-password
+POSTGRES_DB=pitopn
+POSTGRES_HOST=db
+POSTGRES_PORT=5432
+
+# Public URL (set in Dokploy if needed)
+# PUBLIC_URL=https://shop.example.com