fix(artwork): open library-backed artwork through its on-disk root

A library configured with a file:// path stored absRoot as the raw URI, so Abs
produced strings like file:/music/cover.jpg that os.Open/os.Stat reject — folder,
upload and embedded art were treated as dangling on every request, looping forever.
Normalize a file:// path to its parsed OS path (the same root os.DirFS uses);
non-local schemes are left unchanged (out of scope, per the artwork-musicfs TODO).

core/artwork/library_fs.go

@@ -2,7 +2,9 @@ package artwork
 
 import (
 	"context"
+	"net/url"
 	"path/filepath"
+	"strings"
 
 	"github.com/navidrome/navidrome/core/storage"
 	"github.com/navidrome/navidrome/model"
@@ -40,5 +42,18 @@ func loadLibraryView(ctx context.Context, ds model.DataStore, libID int) (librar
 	if err != nil {
 		return libraryView{}, err
 	}
-	return libraryView{FS: fs, absRoot: lib.Path}, nil
+	return libraryView{FS: fs, absRoot: localOSRoot(lib.Path)}, nil
+}
+
+// localOSRoot maps a library path to its on-disk root so Abs() yields paths os.Open/os.Stat accept:
+// a file:// URL becomes its parsed OS path (bare paths already are; non-local schemes stay unchanged).
+func localOSRoot(libPath string) string {
+	if !strings.Contains(libPath, "://") {
+		return libPath
+	}
+	u, err := url.Parse(libPath)
+	if err != nil || u.Scheme != storage.LocalSchemaID {
+		return libPath
+	}
+	return u.Path
 }

core/artwork/library_fs_test.go

@@ -32,6 +32,13 @@ var _ = Describe("loadLibraryView", Ordered, func() {
 		Expect(lib.absRoot).To(Equal("fake:///music"))
 	})
 
+	It("normalizes a library path to an OS root that Abs can join for os.Open/os.Stat", func() {
+		// file:// URLs become their parsed OS path; bare paths and non-local schemes are unchanged.
+		Expect(localOSRoot("file:///music/library")).To(Equal("/music/library"))
+		Expect(localOSRoot("/music/library")).To(Equal("/music/library"))
+		Expect(localOSRoot("fake:///music")).To(Equal("fake:///music"))
+	})
+
 	It("returns an error when the library does not exist", func() {
 		_, err := loadLibraryView(ctx, ds, 999)
 		Expect(err).To(HaveOccurred())