Fix and expand tests: 63 tests passing, covers all core modules

Remove tests/ from .gitignore (was accidentally excluded).

- test_ripper.py: rewrite for current API (_parse_cddb_lines,
  _extract_tracks, _rename_files, _clean_input); fix default quality
- test_organizer.py: update filename assertions (spaces→underscores);
  add TestSanitizeFilename, TestCheckDiscCounts, in-place mode
- test_playlist.py: fix dummy filenames to underscore scheme;
  add multi-disc, filename sanitization, EXTINF and fallback tests

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tests/test_vision_llm.py

@@ -0,0 +1,37 @@
+"""Tests für die Vision-LLM JSON-Extraktion."""
+
+import pytest
+
+from musiksammlung.vision_llm import _extract_json
+
+
+def test_extract_pure_json():
+    text = '{"artist": "Test", "album": "Album"}'
+    assert '"Test"' in _extract_json(text)
+
+
+def test_extract_json_from_markdown_block():
+    text = 'Hier ist das Ergebnis:\n```json\n{"artist": "Test"}\n```\nFertig.'
+    assert '"Test"' in _extract_json(text)
+
+
+def test_extract_json_with_thinking_tags():
+    text = '<think>Ich denke nach...</think>\n{"artist": "Test", "album": "X"}'
+    result = _extract_json(text)
+    assert '"Test"' in result
+
+
+def test_extract_json_with_surrounding_text():
+    text = 'Das JSON:\n{"artist": "A", "album": "B"}\nEnde.'
+    result = _extract_json(text)
+    assert '"A"' in result
+
+
+def test_extract_json_empty_raises():
+    with pytest.raises(ValueError, match="Leere Antwort"):
+        _extract_json("")
+
+
+def test_extract_json_no_json_raises():
+    with pytest.raises(ValueError, match="Kein JSON"):
+        _extract_json("Hier ist kein JSON, nur Text.")