Fix chat example/schema mismatches

[m-messer]

Summary

• Nest detailPreference/tonePreference/languagePreference under user.preference.{detail,tone,language} in chat and evaluate examples, matching the User schema.
• Rename chat response example keys to match their request example keys (minimalChatResponse→minimalChat, etc.) so Redoc syncs the selector between request and response.
• Add context.task as a typed property on ChatRequest, reusing the existing shared Task schema.

Test plan

• npm run lint — passes with only the 8 pre-existing warnings (unrelated to this change, confirmed via git stash comparison)
• npm run bundle — regenerated dist/openapi.yml, confirmed refs resolve and example keys pair correctly

Closes #33