Fix QQ login credential defaults and validation

[caoergou]

Summary

• add optional, data-driven QQ login defaults with the profile number as the account fallback
• require both account and password before click or Enter can submit
• support remembered-password presentation state and keep all login copy localized
• document and export the public configuration, with unit and browser coverage

Root cause

The login panel initialized with empty local state, ignored authored profile credentials, and submitted without validating either field. Hosts therefore could not recreate remembered accounts, while users could enter the simulated client with blank credentials.

Impact

Culture and content authors can prefill a fictional QQ account without putting presentation credentials into the runtime QQ store. Existing profiles remain compatible, and the built-in profile now preselects its QQ number while still requiring a non-empty password.

Validation

• npm run lint
• npm run typecheck:strict
• npx vitest run --maxWorkers=1 --minWorkers=1
• PW_CHROMIUM_PATH=/opt/google/chrome/chrome npx playwright test e2e/qq.spec.ts --project=chromium --workers=1
• npm run build:lib
• npm run size:check

Closes #310