refactor(i18n): move translations to JSON files under app/locales, dynamic language switch

app/routers/web.py

@@ -73,6 +73,9 @@ def _translate_filter(key: str, lang: str = "zh") -> str:
 
 templates.env.filters["t"] = _translate_filter
 
+from app.i18n import get_languages as _get_languages
+templates.env.globals["available_languages"] = _get_languages()
+
 
 def _redirect(url: str) -> RedirectResponse:
     return RedirectResponse(url, status_code=303)