feat: data lifecycle rewrite, download clients, wanted list, and central catalog index

Ships the fresh-start schema cleanup: rebuilt explore catalog index
pipeline (dump import, artifact fetch/build, incremental listen-count
refresh), a new download subsystem (Lidarr/Prowlarr/qBittorrent/SABnzbd/
slskd/yt-dlp providers, staging, reconciliation, wanted list), and the
supporting schema/query/store changes across backend and frontend.

Also includes two smaller follow-ups: bump the central index's
rebuild-after cadence from 90 to 180 days, and remove the Explore
"library only" online/offline toggle entirely (frontend-only, no
backend counterpart) rather than carry unused UI/state.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y2Agd9af5hE7qzti2ackiS

backend/explore/indexjob.go

@@ -153,6 +153,12 @@ func (si *SearchIndex) applyStagesToJob(h *jobs.Handle, status IndexStatus) {
 			phase = t.Name
 			current = int64(t.Completed)
 			total = int64(t.Total)
+
+			// The listens stream's raw completed/total is a bare
+			// percentage; the detail line is what makes it legible.
+			if t.Detail != "" {
+				phase = t.Name + " — " + t.Detail
+			}
 		}
 	}