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

frontend/src/components/sidebar/app-sidebar.ts

@@ -5,7 +5,7 @@ import { designTokens } from '../../styles/tokens.css';
 
 import type { DragActiveDetail } from '@utils/drag-controller';
 
-type View = 'home' | 'playlists' | 'artists' | 'genres' | 'albums' | 'tracks' | 'explore' | 'autotag' | 'jobs' | 'settings';
+type View = 'home' | 'playlists' | 'artists' | 'genres' | 'albums' | 'tracks' | 'explore' | 'wanted' | 'autotag' | 'jobs' | 'settings';
 
 interface NavItem {
     id: View;
@@ -149,6 +149,7 @@ export class AppSidebar extends LitElement {
         { id: 'albums', label: 'Albums', icon: 'compact-disc' },
         { id: 'tracks', label: 'Tracks', icon: 'music' },
         { id: 'explore', label: 'Explore', icon: 'globe' },
+        { id: 'wanted', label: 'Wanted', icon: 'bookmark' },
         { id: 'autotag', label: 'Autotag', icon: 'tag' },
         { id: 'jobs', label: 'Jobs', icon: 'list-check' },
         { id: 'settings', label: 'Settings', icon: 'gear' },