feat: autotag mixed-bag splitting, search relevance fixes, and multi-library download imports

Autotag: detect "junk drawer" folders with no artist/album consensus
and split them into synthetic per-cluster groups instead of forcing
one match on an unrelated pile of tracks; repair tagging_items rows
left behind by a prior scan orphan-cleanup gap.

Explore: fix an exact artist-name search being drowned out by its own
catalog entries in intent-prior scoring, and prune stale in_library
bookkeeping left behind when a referenced library row is deleted.

Download: fix a multi-library regression where every import failed
with "no library root configured" — the importer resolved the
library root from a legacy single-library config field that nothing
populates in the current multi-library model. It now resolves the
destination library per-request from the request's own library_id.
Also widen the Soulseek search window (12s -> 20s), measured against
real request history to be missing available peers on live queries.

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

frontend/wailsjs/go/library/Library.d.ts

@@ -57,6 +57,8 @@ export function IsScanActive():Promise<boolean>;
 
 export function IsScanPaused():Promise<boolean>;
 
+export function LibraryPath(arg1:number):Promise<string>;
+
 export function PauseScan():Promise<void>;
 
 export function QueuedLibraryNames():Promise<Array<string>>;

frontend/wailsjs/go/library/Library.js

@@ -106,6 +106,10 @@ export function IsScanPaused() {
   return window['go']['library']['Library']['IsScanPaused']();
 }
 
+export function LibraryPath(arg1) {
+  return window['go']['library']['Library']['LibraryPath'](arg1);
+}
+
 export function PauseScan() {
   return window['go']['library']['Library']['PauseScan']();
 }