feat: mock payment flow + flash token page (test mode)

- Mock purchase: order create → mock-pay → FlashToken issued instantly (no real billing)
- Flash page (/flash/:token): esp-web-tools integration, token state display, consume on complete
- Orders route: create/mock-pay/me/refund with full audit logging
- Flash route: GET validate, GET manifest (esp-web-tools compatible), POST consume
- MinIO file proxy (/api/files/*): browser CORS solved, firmware served through backend
- Schema: chipFamily on Project, flashOffset on ProjectFile
- ProjectNew: chipFamily selector + firmware flash offset option
- MyOrders: real order list with flash token status and buttons
- Dockerfile: prisma db push (no migration files needed for dev)
- TOSS_PAYMENT_GUIDE.md: step-by-step guide for real payment after business registration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

platform/backend/Dockerfile

@@ -15,5 +15,5 @@ COPY src ./src
 
 EXPOSE 3201
 
-# 마이그레이션 후 서버 시작
-CMD ["sh", "-c", "npx prisma migrate deploy && node src/index.js"]
+# prisma db push: 마이그레이션 파일 없이 스키마를 DB에 직접 동기화 (개발용)
+CMD ["sh", "-c", "npx prisma db push --accept-data-loss && node src/index.js"]