refactor: Update playlist service and endpoints for global current playlist management

tests/api/v1/test_playlist_endpoints.py

@@ -358,14 +358,14 @@ class TestPlaylistEndpoints:
         assert data["genre"] == "jazz"
 
     @pytest.mark.asyncio
-    async def test_update_playlist_set_current(
+    async def test_update_playlist_basic_fields(
         self,
         authenticated_client: AsyncClient,
         test_session: AsyncSession,
         test_user: User,
     ) -> None:
-        """Test PUT /api/v1/playlists/{id} - set playlist as current."""
-        # Create test playlists within this test
+        """Test PUT /api/v1/playlists/{id} - update basic fields only."""
+        # Create test playlist
         user_id = test_user.id
         test_playlist = Playlist(
             user_id=user_id,
@@ -377,25 +377,13 @@ class TestPlaylistEndpoints:
             is_deletable=True,
         )
         test_session.add(test_playlist)
-
-        # Note: main_playlist doesn't need to be current=True for this test
-        # The service logic handles current playlist management
-        main_playlist = Playlist(
-            user_id=None,
-            name="Main Playlist",
-            description="Main playlist",
-            is_main=True,
-            is_current=False,
-            is_deletable=False,
-        )
-        test_session.add(main_playlist)
         await test_session.commit()
         await test_session.refresh(test_playlist)
 
         # Extract ID before HTTP request
         playlist_id = test_playlist.id
 
-        payload = {"is_current": True}
+        payload = {"name": "Updated Playlist", "description": "Updated description"}
 
         response = await authenticated_client.put(
             f"/api/v1/playlists/{playlist_id}", json=payload,
@@ -403,7 +391,10 @@ class TestPlaylistEndpoints:
 
         assert response.status_code == 200
         data = response.json()
-        assert data["is_current"] is True
+        assert data["name"] == "Updated Playlist"
+        assert data["description"] == "Updated description"
+        # is_current should remain unchanged (not handled by this endpoint)
+        assert data["is_current"] is False
 
     @pytest.mark.asyncio
     async def test_delete_playlist_success(