simplify language selector display to use text-only labels

Replace icon-based language options with plain text labels in both the
header dropdown and preferences settings to keep the UI clean and
avoid potential controversies. Remove unused country-flag-icons dependency.

web/package.json

@@ -12,7 +12,6 @@
     "@visactor/vchart-semi-theme": "~1.8.8",
     "axios": "1.12.0",
     "clsx": "^2.1.1",
-    "country-flag-icons": "^1.5.19",
     "dayjs": "^1.11.11",
     "history": "^5.3.0",
     "i18next": "^23.16.8",