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

go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/go-flac/go-flac/v2 v2.0.4
 	github.com/godbus/dbus/v5 v5.1.0
 	github.com/golang-cz/devslog v0.0.15
+	github.com/google/uuid v1.6.0
 	github.com/gopxl/beep/v2 v2.1.1
 	github.com/klauspost/compress v1.17.9
 	github.com/parquet-go/parquet-go v0.30.1
@@ -158,7 +159,6 @@ require (
 	github.com/google/cel-go v0.26.1 // indirect
 	github.com/google/go-cmp v0.7.0 // indirect
 	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510 // indirect
-	github.com/google/uuid v1.6.0 // indirect
 	github.com/gookit/color v1.6.0 // indirect
 	github.com/gordonklaus/ineffassign v0.2.0 // indirect
 	github.com/gorilla/css v1.0.1 // indirect