feat: add new-user style quiz onboarding engine for miniapp

[leeekyrie]

Summary

• add backend onboarding engine tables, services, and APIs for style-quiz flow
• add style answer mapper + non-blocking AI style insight fallback
• add miniapp blocking onboarding gate + style quiz modal and full preferences editing in settings

Test Plan

• backend: TEST_DATABASE_URL='postgresql+asyncpg://bytedance@127.0.0.1:5432/wardrobe_test' .venv/bin/pytest tests/test_style_quiz_mapper.py tests/test_onboarding.py -q
• backend: TEST_DATABASE_URL='postgresql+asyncpg://bytedance@127.0.0.1:5432/wardrobe_test' .venv/bin/pytest tests/test_auth.py tests/test_preferences.py -q
• miniapp: pnpm typecheck
• miniapp: TARO_APP_API_BASE_URL=http://localhost:8000 pnpm build:weapp