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/library/scan_control.go

@@ -3,8 +3,6 @@ package library
 import (
 	"context"
 
-	"github.com/wailsapp/wails/v2/pkg/runtime"
-
 	"yellowjacket/backend/events"
 	"yellowjacket/backend/jobs"
 )
@@ -41,7 +39,7 @@ func (l *Library) PauseScan() {
 	reg := l.jobs
 	l.mu.Unlock()
 
-	runtime.EventsEmit(l.ctx, events.LibraryScanPaused)
+	l.emit(events.LibraryScanPaused)
 
 	// Confirm the pause on the job — the registry moved it to "pausing"
 	// when the request came in.  Writing the durable pause record is a
@@ -76,7 +74,7 @@ func (l *Library) ResumeScan() {
 	reg := l.jobs
 	l.mu.Unlock()
 
-	runtime.EventsEmit(l.ctx, events.LibraryScanResumed)
+	l.emit(events.LibraryScanResumed)
 
 	// Clears the durable pause record as a side effect of leaving
 	// StatePaused.