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

cmd/indexbuild/decide_test.go

@@ -1,3 +1,5 @@
+//go:build indexbuild
+
 package main
 
 import (

cmd/indexbuild/main.go

@@ -1,3 +1,5 @@
+//go:build indexbuild
+
 // Command indexbuild maintains the explore search index outside the
 // desktop app, so the catalog can be built once centrally instead of by
 // every install.
@@ -9,7 +11,7 @@
 //	import older than 3mo    → rebuild (re-import from the newest dump)
 //	otherwise                → refresh (fold in new incremental listens)
 //
-// A full build streams ~205GB from the ListenBrainz spark dump — far
+// A full build streams ~89GB from the ListenBrainz spark dump — far
 // more than one CI job should attempt — so builds are budgeted and
 // resumable: the importer checkpoints its absolute stream offset, and
 // each run continues where the last stopped. A refresh is cheap
@@ -87,7 +89,7 @@ func main() {
 			"stop and checkpoint a build after this long (0 = no limit)")
 		modeFlag = flag.String("mode", string(modeAuto),
 			"auto | build | refresh | rebuild")
-		rebuildAfter = flag.Duration("rebuild-after", 90*24*time.Hour,
+		rebuildAfter = flag.Duration("rebuild-after", 180*24*time.Hour,
 			"re-import from a fresh dump once the last import is older than this")
 		refreshAfter = flag.Duration("refresh-after", 7*24*time.Hour,
 			"minimum gap between incremental refreshes (0 = always)")