fix(search): the live-search tooltip says what a search costs

It always said a live search spends the shared API quota, while the default source (the website's
own endpoint, scrape) spends none — the owner avoided a free search because of it. /api/me now names
the running search_source, and the tooltip names the cost under it: none for scrape (the enrich step
costs a unit or two), 100 units a page for the official API.

backend/app/routes/me.py

@@ -148,6 +148,9 @@ def get_me(
         "google_enabled": google_enabled(db),
         # Whether the optional Plex module is enabled (UI shows the Plex feed source when so).
         "plex_enabled": sysconfig.get_bool(db, "plex_enabled"),
+        # Which live-search source runs, so the search button can say what a search costs: "scrape"
+        # spends no API quota, "api" spends 100 units a page.
+        "search_source": sysconfig.get_str(db, "search_source"),
         "can_read": has_read_scope(user),
         "can_write": has_write_scope(user),
         "pending_invites": pending_invites,