feat: multi-source artist images with thumbnails + grid integration

Complete rewrite of the artist image pipeline:

STORAGE:
- Migration 16: artist_images table tracking source, URL, path,
  primary flag, dimensions per image (up to 10 per artist)
- Directory structure: artist-images/{mbid[:2]}/{mbid}/ with
  primary.jpg + primary_sm.jpg/_md.jpg/_lg.jpg thumbnails
- Miss marker (.miss file) prevents re-fetching artists with no image

SOURCES (priority order):
1. MusicBrainz direct image relations (Wikimedia Commons)
2. Wikidata P18 property (Wikimedia Commons)
3. Wikipedia lead image (NEW — via Wikidata sitelinks → Wikipedia API)

Each source is checked, deduplicated, and the first available
image becomes the primary with sm/md/lg thumbnail generation
(100px/200px/400px, matching cover art tier sizes).

ASSET SERVING:
- /artist-images/ path registered with Wails asset handler
- Serves files via http.FileServer from the artist-images directory
- Same pattern as /covers/ for cover art

ARTIST MODEL:
- Artist struct gains ImageSmall/ImageMedium/ImageLarge fields
- resolveArtistImages does bulk MBID lookup → disk stat for each
- Populated in GetAllArtists and GetAllArtistsByLibrary

GRID VIEW:
- artists-view uses model URLs directly (no more base64 data URLs)
- Size selection based on imageSize * devicePixelRatio (like cover-grid)
- Removed batch GetArtistImages call and in-memory cache — no longer needed

backend/library/query.go

@@ -4,12 +4,15 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"os"
+	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
 
 	"yellowjacket/backend/coverart"
 	"yellowjacket/backend/database/sql/sqlcgen"
+	"yellowjacket/backend/system"
 )
 
 // Sentinel errors for library queries.
@@ -142,8 +145,11 @@ func (l *Library) GetTrackMBIDs(filePath string) TrackMBIDs {
 
 // Artist represents an artist in the library.
 type Artist struct {
-	ID   int64
-	Name string
+	ID          int64
+	Name        string
+	ImageSmall  string
+	ImageMedium string
+	ImageLarge  string
 }
 
 // Album represents an album for the cover grid display.
@@ -366,9 +372,69 @@ func (l *Library) GetAllArtists() ([]Artist, error) {
 		})
 	}
 
+	// Resolve artist image URLs from the disk cache.
+	l.resolveArtistImages(artists)
+
 	return artists, nil
 }
 
+// resolveArtistImages populates ImageSmall/Medium/Large for artists
+// that have cached images on disk.  Does a bulk MBID lookup from the
+// artists table, then checks the artist-images directory for each.
+func (l *Library) resolveArtistImages(artists []Artist) {
+	if len(artists) == 0 {
+		return
+	}
+
+	dataDir, err := system.GetUserDataDirPath()
+	if err != nil {
+		return
+	}
+
+	baseDir := filepath.Join(dataDir, "artist-images")
+
+	// Bulk load name→mbid from the artists table.
+	rows, err := l.db.QueryContext(
+		"SELECT name, mbid FROM artists WHERE mbid IS NOT NULL AND mbid != ''",
+	)
+	if err != nil {
+		return
+	}
+
+	defer func() { _ = rows.Close() }()
+
+	mbidMap := make(map[string]string)
+
+	for rows.Next() {
+		var name, mbid string
+		if err := rows.Scan(&name, &mbid); err == nil {
+			mbidMap[name] = mbid
+		}
+	}
+
+	for i := range artists {
+		mbid, ok := mbidMap[artists[i].Name]
+		if !ok || len(mbid) < 2 {
+			continue
+		}
+
+		dir := filepath.Join(baseDir, mbid[:2], mbid)
+		prefix := "/artist-images/" + mbid[:2] + "/" + mbid + "/"
+
+		if _, err := os.Stat(filepath.Join(dir, "primary_sm.jpg")); err == nil {
+			artists[i].ImageSmall = prefix + "primary_sm.jpg"
+		}
+
+		if _, err := os.Stat(filepath.Join(dir, "primary_md.jpg")); err == nil {
+			artists[i].ImageMedium = prefix + "primary_md.jpg"
+		}
+
+		if _, err := os.Stat(filepath.Join(dir, "primary_lg.jpg")); err == nil {
+			artists[i].ImageLarge = prefix + "primary_lg.jpg"
+		}
+	}
+}
+
 // GetAlbumsByArtist returns all albums where the given artist is the album artist.
 func (l *Library) GetAlbumsByArtist(
 	artistID int64,
@@ -646,6 +712,8 @@ func (l *Library) GetAllArtistsByLibrary(
 		})
 	}
 
+	l.resolveArtistImages(artists)
+
 	return artists, nil
 }