Opus/M4A-Cover-Embedding, cover.py-Tests und OCR-Tests

- tagger.py: embed_cover() unterstützt jetzt .opus (Vorbis-Comment
  METADATA_BLOCK_PICTURE) und .m4a (MP4Cover); imports ergänzt
- test_tagger.py: 2 neue Tests für Opus/M4A; minimale Audio-Fixtures
  als base64-Konstanten (176 B Opus, 856 B M4A)
- test_cover.py: TestPrepareCover (5 Tests) und TestCopyCovers (6 Tests)
  für prepare_cover() und copy_covers()
- test_ocr.py: 13 Tests für run_ocr(), _detect_and_fix_rotation()
  und ocr_images(); Tesseract via subprocess.run gemockt

144 Tests, 0 Fehler

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

src/musiksammlung/tagger.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import base64
 import io
 import logging
 from pathlib import Path
@@ -9,6 +10,8 @@ from pathlib import Path
 from mutagen import File as MutagenFile
 from mutagen.flac import FLAC, Picture
 from mutagen.id3 import APIC, ID3, ID3NoHeaderError
+from mutagen.mp4 import MP4, MP4Cover
+from mutagen.oggopus import OggOpus
 from PIL import Image
 
 from musiksammlung.models import Album, Disc, Track
@@ -127,6 +130,24 @@ def embed_cover(audio_path: Path, cover_path: Path) -> None:
         ))
         audio.save(str(audio_path))
 
+    elif suffix == ".opus":
+        audio = OggOpus(str(audio_path))
+        pic = Picture()
+        pic.type = 3  # Front cover
+        pic.mime = mime
+        pic.data = cover_data
+        pic.width = 0
+        pic.height = 0
+        pic.depth = 0
+        pic.colors = 0
+        audio["metadata_block_picture"] = [base64.b64encode(pic.write()).decode("ascii")]
+        audio.save()
+
+    elif suffix == ".m4a":
+        audio = MP4(str(audio_path))
+        audio["covr"] = [MP4Cover(cover_data, imageformat=MP4Cover.FORMAT_JPEG)]
+        audio.save()
+
     else:
         logger.debug("Cover-Embedding für %s nicht unterstützt", suffix)
         return