feat: harden web UI system

[thonatos]

Summary

OpenSpec

• This PR implements an OpenSpec change: 2026-08-02-realign-web-design-system
• No OpenSpec change is needed (small doc/fix, no shipped behavior change).

Verification

• pnpm verify passed.
• A subset was run instead: <!-- commands --> because <!-- reason -->.

Impact Checklist

• App code (apps/, packages/)
• API behavior / OpenAPI contract (apps/api/src/routes/*.ts zod-openapi declarations, api/openapi.json via pnpm gen:openapi)
• Database schema or migration (packages/db)
• Deployment (deployment/)
• Documentation (README.md, docs/, wiki/)
• CI / scripts (.github/workflows/, scripts/, package.json)
• Secret handling: no real .env, tokens, cookies, private keys, database URLs, or user data committed.

Migration / Deployment Notes

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