Add phone-based EAN scanning, scanner server for cover upload, Vision-LLM integration

New features:
- EAN/Barcode can now be entered by typing or by photographing the CD sleeve;
  Vision-LLM (extract_barcode_from_image) reads the barcode from the photo
- Scanner server (port 8765) starts at the beginning of every album loop,
  serving both EAN barcode scanning and back cover upload via QR code
- Vision-LLM analyses back cover in background thread while ripping;
  priority: Vision-LLM > MusicBrainz > CDDB
- _find_abcde_mbid reads MBID from abcde temp dirs for CAA cover download
  even when the CD barcode is not linked in MusicBrainz
- Concrete copy-paste apply commands shown after each album in 'Next steps'
- _sanitize_name: whitelist approach (removes brackets and punctuation)
- qrcode added as dependency for terminal QR code display

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

tests/test_cover.py

@@ -1,10 +1,13 @@
 """Tests für Cover-Funktionen."""
 
+from io import BytesIO
 from pathlib import Path
+from unittest.mock import MagicMock, patch
 
+import httpx
 from PIL import Image
 
-from musiksammlung.cover import copy_covers, find_cover, prepare_cover
+from musiksammlung.cover import copy_covers, download_caa_covers, find_cover, prepare_cover
 
 
 def _make_image(path: Path, size: tuple[int, int] = (100, 100), mode: str = "RGB") -> Path:
@@ -119,3 +122,90 @@ class TestCopyCovers:
         original_mtime = existing.stat().st_mtime
         copy_covers(None, None, tmp_path)
         assert (tmp_path / "frontcover.jpg").stat().st_mtime == original_mtime
+
+
+def _fake_image_bytes() -> bytes:
+    """Erzeugt ein gültiges JPEG-Bild als bytes."""
+    buf = BytesIO()
+    Image.new("RGB", (200, 200), (100, 150, 200)).save(buf, "JPEG")
+    return buf.getvalue()
+
+
+def _mock_caa_response(status_code: int = 200, content: bytes = b"") -> MagicMock:
+    """Erstellt ein Mock-httpx.Response für CAA-Requests."""
+    resp = MagicMock(spec=httpx.Response)
+    resp.status_code = status_code
+    resp.content = content
+    resp.raise_for_status.return_value = None
+    return resp
+
+
+class TestDownloadCaaCovers:
+    """Tests für download_caa_covers."""
+
+    def test_downloads_front_and_back(self, tmp_path: Path) -> None:
+        """Beide Cover werden heruntergeladen und als JPEG gespeichert."""
+        img_bytes = _fake_image_bytes()
+        resp = _mock_caa_response(200, img_bytes)
+
+        with patch("musiksammlung.cover.httpx.get", return_value=resp):
+            download_caa_covers("test-mbid", tmp_path)
+
+        assert (tmp_path / "frontcover.jpg").exists()
+        assert (tmp_path / "backcover.jpg").exists()
+        # Ergebnis ist ein gültiges JPEG
+        assert Image.open(tmp_path / "frontcover.jpg").format == "JPEG"
+
+    def test_404_skips_cover(self, tmp_path: Path) -> None:
+        """404 → kein Cover, kein Fehler."""
+        resp_404 = _mock_caa_response(404)
+
+        with patch("musiksammlung.cover.httpx.get", return_value=resp_404):
+            download_caa_covers("no-cover-mbid", tmp_path)
+
+        assert not (tmp_path / "frontcover.jpg").exists()
+        assert not (tmp_path / "backcover.jpg").exists()
+
+    def test_http_error_continues(self, tmp_path: Path) -> None:
+        """Netzwerkfehler → Warnung, kein Abbruch."""
+        with patch(
+            "musiksammlung.cover.httpx.get",
+            side_effect=httpx.HTTPError("timeout"),
+        ):
+            download_caa_covers("error-mbid", tmp_path)
+
+        assert not (tmp_path / "frontcover.jpg").exists()
+        assert not (tmp_path / "backcover.jpg").exists()
+
+    def test_skips_existing_cover(self, tmp_path: Path) -> None:
+        """Bereits vorhandene Cover werden nicht überschrieben."""
+        existing = _make_image(tmp_path / "frontcover.jpg")
+        original_size = existing.stat().st_size
+
+        img_bytes = _fake_image_bytes()
+        resp = _mock_caa_response(200, img_bytes)
+
+        with patch("musiksammlung.cover.httpx.get", return_value=resp) as mock_get:
+            download_caa_covers("test-mbid", tmp_path)
+
+        # frontcover.jpg bleibt unverändert
+        assert (tmp_path / "frontcover.jpg").stat().st_size == original_size
+        # backcover.jpg wird heruntergeladen (war nicht vorhanden)
+        assert (tmp_path / "backcover.jpg").exists()
+        # Nur ein HTTP-Request (für back), nicht zwei
+        assert mock_get.call_count == 1
+
+    def test_front_only_on_back_404(self, tmp_path: Path) -> None:
+        """Front 200, Back 404 → nur frontcover.jpg erstellt."""
+        img_bytes = _fake_image_bytes()
+        resp_ok = _mock_caa_response(200, img_bytes)
+        resp_404 = _mock_caa_response(404)
+
+        with patch(
+            "musiksammlung.cover.httpx.get",
+            side_effect=[resp_ok, resp_404],
+        ):
+            download_caa_covers("mixed-mbid", tmp_path)
+
+        assert (tmp_path / "frontcover.jpg").exists()
+        assert not (tmp_path / "backcover.jpg").exists()