v0.24.0: click the blank cover

Clicking the gray sidebar art square (playing track has no embedded art)
now opens Download Album Art for that track, same as the right-click menu.
Once art is embedded the square refreshes and a click opens the big view
again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_round61.py

@@ -0,0 +1,63 @@
+"""Round 61: clicking the gray (art-less) sidebar square asks for the
+playing track's art to be downloaded; with art it still opens the big view."""
+
+from PyQt6.QtCore import Qt
+from PyQt6.QtGui import QPixmap
+
+from lintunes.models import Track
+from tests.test_round49 import _FakePlayer, _release
+
+
+def _art():
+    from lintunes.gui.sidebar import SidebarArt
+    art = SidebarArt(_FakePlayer())
+    art.resize(100, 100)
+    requested = []
+    art.download_art_requested.connect(requested.append)
+    return art, requested
+
+
+def _track(tid=7):
+    # No location: set_track reads no art, which is the gray-square case
+    return Track(track_id=tid, name="Song", artist="Artist", album="Album")
+
+
+class TestGraySquareClick:
+    def test_click_without_art_requests_a_download(self, qapp):
+        art, requested = _art()
+        art.set_track(_track(42))
+        art.mouseReleaseEvent(_release(Qt.MouseButton.LeftButton))
+        assert requested == [42]
+        assert not art._art_window.isVisible()
+
+    def test_no_track_requests_nothing(self, qapp):
+        art, requested = _art()
+        art.mouseReleaseEvent(_release(Qt.MouseButton.LeftButton))
+        assert requested == []
+
+    def test_with_art_opens_the_big_view_instead(self, qapp):
+        art, requested = _art()
+        art.set_track(_track())
+        pixmap = QPixmap(32, 32)
+        pixmap.fill(Qt.GlobalColor.blue)
+        art._pixmap = pixmap
+        art.mouseReleaseEvent(_release(Qt.MouseButton.LeftButton))
+        try:
+            assert requested == []
+            assert art._art_window.isVisible()
+        finally:
+            art._art_window.hide()
+
+    def test_right_click_or_release_outside_requests_nothing(self, qapp):
+        art, requested = _art()
+        art.set_track(_track())
+        art.mouseReleaseEvent(_release(Qt.MouseButton.RightButton))
+        art.mouseReleaseEvent(_release(Qt.MouseButton.LeftButton, 500, 500))
+        assert requested == []
+
+    def test_tooltip_says_what_a_click_will_do(self, qapp):
+        art, _ = _art()
+        art.set_track(None)
+        assert art.toolTip() == ""
+        art.set_track(_track())
+        assert art.toolTip() == "Click to download album art"