Find cover in parent directory when album_dir is a CD subdirectory

When applying in-place with input_dir=CD1, cover files naturally live
in the album root (parent). Fall back to searching the parent when
album_dir matches the CD\d+ pattern and no cover is found in-place.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/musiksammlung/cli.py

@@ -299,6 +299,9 @@ def apply(
     tag_album(album, album_dir)
     copy_covers(front, back, album_dir)
     cover = find_cover(album_dir)
+    # Bei in-place mit CD-Unterverzeichnis auch im Album-Root nach Cover suchen
+    if cover is None and _CD_SUBDIR.match(album_dir.resolve().name):
+        cover = find_cover(album_dir.resolve().parent)
     if cover:
         typer.echo(f"Bette Cover ein ({cover.name})...")
         embed_album_cover(album, album_dir, cover)