Fix sanitize_filename consistency, add scanner server tests, remove stray file

- Unify sanitize_filename (organizer) and _sanitize_name (ripper): both now use
  whitelist approach — spaces→underscore, keep \w and hyphens, remove everything
  else (brackets, punctuation, commas, dots, …). _sanitize_name removed from
  ripper.py; ripper now imports sanitize_filename from organizer directly.
- Add tests/test_scanner_server.py: 15 tests covering HTTP GET/POST handlers,
  image upload queue, 404/400 error paths, _get_local_ip fallback, print_qr
  graceful degradation without qrcode installed.
- Delete empty stray file '3' from repo root.

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

tests/test_ripper.py

@@ -5,6 +5,7 @@ from unittest.mock import MagicMock, patch
 
 from musiksammlung.config import AudioFormat
 from musiksammlung.models import Album, Disc, Track, TrackInfo
+from musiksammlung.organizer import sanitize_filename
 from musiksammlung.ripper import (
     RipperConfig,
     _clean_input,
@@ -12,38 +13,37 @@ from musiksammlung.ripper import (
     _parse_cddb_lines,
     _parse_grab_tracks,
     _rename_files,
-    _sanitize_name,
     interactive_rip,
 )
 
 
 class TestSanitizeName:
-    """Tests für _sanitize_name."""
+    """Tests für sanitize_filename (aus organizer, genutzt von ripper und apply)."""
 
     def test_replace_spaces(self) -> None:
-        assert _sanitize_name("Hello World") == "Hello_World"
-        assert _sanitize_name("Test Track Title") == "Test_Track_Title"
+        assert sanitize_filename("Hello World") == "Hello_World"
+        assert sanitize_filename("Test Track Title") == "Test_Track_Title"
 
     def test_remove_invalid_chars(self) -> None:
-        assert _sanitize_name("Test/Track:Name") == "TestTrackName"
-        assert _sanitize_name('Test<Track>"Name') == "TestTrackName"
-        assert _sanitize_name("Test|Track?Name*") == "TestTrackName"
-        assert _sanitize_name("It's_a_Test") == "Its_a_Test"
+        assert sanitize_filename("Test/Track:Name") == "TestTrackName"
+        assert sanitize_filename('Test<Track>"Name') == "TestTrackName"
+        assert sanitize_filename("Test|Track?Name*") == "TestTrackName"
+        assert sanitize_filename("It's_a_Test") == "Its_a_Test"
 
     def test_remove_brackets_and_punctuation(self) -> None:
-        assert _sanitize_name("Best of (1990)") == "Best_of_1990"
-        assert _sanitize_name("Hello, World!") == "Hello_World"
-        assert _sanitize_name("Vol. 2") == "Vol_2"
-        assert _sanitize_name("Salt & Pepper [Remix]") == "Salt_Pepper_Remix"
-        assert _sanitize_name("The Best of... (Deluxe Edition)") == "The_Best_of_Deluxe_Edition"
+        assert sanitize_filename("Best of (1990)") == "Best_of_1990"
+        assert sanitize_filename("Hello, World!") == "Hello_World"
+        assert sanitize_filename("Vol. 2") == "Vol_2"
+        assert sanitize_filename("Salt & Pepper [Remix]") == "Salt_Pepper_Remix"
+        assert sanitize_filename("The Best of... (Deluxe Edition)") == "The_Best_of_Deluxe_Edition"
 
     def test_keep_umlauts(self) -> None:
-        assert _sanitize_name("Grüße aus Österreich") == "Grüße_aus_Österreich"
-        assert _sanitize_name("Schöne Sänger") == "Schöne_Sänger"
+        assert sanitize_filename("Grüße aus Österreich") == "Grüße_aus_Österreich"
+        assert sanitize_filename("Schöne Sänger") == "Schöne_Sänger"
 
     def test_strip_underscores(self) -> None:
-        assert _sanitize_name("_Test_") == "Test"
-        assert _sanitize_name("  _Test_  ") == "Test"
+        assert sanitize_filename("_Test_") == "Test"
+        assert sanitize_filename("  _Test_  ") == "Test"
 
 
 class TestCleanInput: