feat(search): drop quota wording when the live search source is scrape

The search response now reports its source; in scrape mode (zero quota) the
results banner and Load-more button drop the 'uses quota' wording. Adds the
search_source toggle's labels/hints and updates the per-user-limit hint to note
the cost only applies to the api source. EN/HU/DE.

frontend/src/i18n/locales/en/feed.json

@@ -41,10 +41,12 @@
     "searchFor": "Search YouTube for “{{query}}”",
     "resultsFor": "YouTube results for “{{query}}”",
     "quotaNote": "Live results — uses shared API quota",
+    "freeNote": "Live results — no search quota used",
     "back": "Back to feed",
     "searching": "Searching YouTube…",
     "noResults": "No YouTube videos found.",
     "error": "YouTube search failed.",
-    "loadMore": "Load more (uses quota)"
+    "loadMore": "Load more (uses quota)",
+    "loadMoreFree": "Load more"
   }
 }