chore: add .env.example with all environment variables

.env.example

@@ -0,0 +1,30 @@
+# FarmaFinder Environment Variables
+
+# PostgreSQL
+PG_PASSWORD=change-me-in-production
+
+# Backend
+SESSION_SECRET=change-me-in-production
+CORS_ORIGIN=http://localhost:4000
+FARMACIAS_WEBHOOK_URL=
+
+# Redis
+REDIS_PASSWORD=
+
+# N8N Workflow Automation
+N8N_USER=admin
+N8N_PASSWORD=change-me
+N8N_EMAIL=admin@farmafinder.com
+
+# Parapharmacy API
+PARAPHARMACY_API_URL=http://parapharmacy-api:3002
+MONGODB_URI=mongodb://mongodb:27017/parapharmacy
+
+# Expo Push Notifications (mobile)
+EXPO_ACCESS_TOKEN=
+
+# OpenTelemetry
+VITE_FARO_ENDPOINT=http://localhost:4318
+VITE_FARO_APP_NAME=farmafinder-frontend
+VITE_FARO_ENV=production
+VITE_FARO_APP_VERSION=1.0.0