feat: add react-i18next with English and Hindi locale support.

- Add i18next + react-i18next + i18next-browser-languagedetector.
- EN/HI translation files covering all UI strings across every page and component.
- Language switcher button in Navbar; choice persisted to localStorage.
- document.documentElement.lang synced to active language in App.
- Skip-nav link and #main-content anchor for keyboard accessibility.
- aria-describedby on modal dialog; page title and meta description in index.html.
- Secure page title set to 'BIS SP-21 Standards.'

web/client/package.json

@@ -10,8 +10,11 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "i18next": "^26.0.8",
+    "i18next-browser-languagedetector": "^8.2.1",
     "react": "^19.2.5",
     "react-dom": "^19.2.5",
+    "react-i18next": "^17.0.6",
     "react-router-dom": "^7.14.2"
   },
   "devDependencies": {