feat(web): add typed Next.js care-plan product application

[mimosapudical]

Summary

• Add a strict TypeScript and Next.js product interface for asynchronous care-plan creation, status polling, search, detail views, and downloads.
• Add Node.js backend-for-frontend routes with Zod validation against the existing Django API contracts.
• Integrate frontend tests, production builds, GitHub Actions, Docker Compose, and updated architecture documentation.

Verification

Previously verified locally: ESLint, TypeScript type checking, 8 Vitest tests, Next.js production build, and git diff --check.

This pull request runs the complete repository CI, including existing Django/Python and Go operator checks plus the new frontend quality gate, before merging into dev.