fix: resolve locale for logged-out visitors from browser/localStorage

[bakill3]

Problem:

Logged-out visitors always see English because useUserLocale returned early when userGeneralSetting was undefined, and i18n.init()had no lng set (the detection config referenced a plugin that was never loaded).

Fix:

• i18n.ts: resolve initial locale at module load (query param → localStorage → navigator.languages → "en") so the first render is correct.
• useUserLocale.ts: remove early return → run getLocaleWithFallback() for all users.
• utils/i18n.ts: add normalizeLocale() helper, query param support, and navigator.languages iteration.

Locale priority (both logged-in and logged-out):

1. ?locale=xx query parameter
2. User setting (authenticated only)
3. localStorage("memos-locale")
4. navigator.languages
5. "en"