fix(review): address CodeRabbit feedback

- swap direct i18next t imports for the useTranslation hook so the four
  touched components re-render on language change
- localize the buffer seconds unit via a buffer_seconds key instead of a
  literal trailing s
- reword the useAppRouter guard comment to match its real scope

translations/en.json

@@ -631,7 +631,7 @@
       "audio": "Audio:",
       "subtitle": "Subtitle:",
       "bitrate": "Bitrate:",
-      "buffer": "Buffer:",
+      "buffer_seconds": "Buffer: {{seconds}}s",
       "vo": "VO:",
       "dropped_frames": "Dropped: {{count}} frames",
       "loading": "Loading..."