v0.31.1: one button look — crisper emboss, darken on hover

- The emboss hugs the edges: thin lit and shaded rims, a defined outline
  that's a touch darker along the bottom, and a nearly flat face — shape
  without depth.
- Hover darkens the whole button slightly instead of Qt's pale panel on
  top of it.
- One face for every button (theme.button_face_qss): regular buttons,
  Library and its ▾, the purple friend-mode buttons, and the transport
  boxes. Shuffle and bpm are boxes that are one button, so the whole box
  darkens (bpm's whole box is now its tap target); the play box's three
  tiles each darken on their own.

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

tests/test_round63.py

@@ -137,9 +137,37 @@ class TestEmboss:
         color = QColor("#808080")
         up = theme.emboss_gradient(color)
         down = theme.emboss_gradient(color, pressed=True)
-        light = color.lighter(theme.EMBOSS_LIGHTER).name()
-        assert up.index(light) < up.index("stop:1")
-        assert down.index(light) > down.index("stop:1")
+        rim = color.lighter(theme.EMBOSS_RIM).name()
+        assert up.startswith(f"qlineargradient(x1:0, y1:0, x2:0, y2:1, stop:0 {rim}")
+        assert down.endswith(f"stop:1 {rim})")
+
+    def test_crisp_rims_hug_the_edges(self):
+        """The shape lives in thin rims, not a wide soft slope."""
+        gradient = theme.emboss_gradient(QColor("#808080"))
+        assert f"stop:{theme.EMBOSS_RIM_WIDTH} " in gradient
+        assert theme.EMBOSS_RIM_WIDTH <= 0.1
+        assert theme.EMBOSS_RIM > theme.EMBOSS_LIGHTER
+
+    def test_hover_darkens_the_whole_button(self):
+        color = QColor("#c0c0c0")
+        qss = theme.button_face_qss("QPushButton", color)
+        hover = qss.split("QPushButton:hover {", 1)[1].split("}", 1)[0]
+        assert f"stop:0.5 {color.darker(theme.HOVER_DARKER).name()}" in hover
+
+    def test_every_button_shares_the_face(self, qapp):
+        from unittest.mock import MagicMock
+        from lintunes.gui.sidebar import SidebarPanel
+        from lintunes.gui.transport import _box_style
+        from lintunes.gui import cassette_art
+        manager = MagicMock()
+        manager.library.playlists = {}
+        sidebar = SidebarPanel(manager, MagicMock())
+        for qss in (sidebar.library_button.styleSheet(),
+                    sidebar.friend_button.styleSheet(),
+                    _box_style(QColor("#dddddd"), button=True),
+                    cassette_art.friend_button_qss()):
+            assert ":hover" in qss
+            assert "border-bottom-color" in qss
 
     def test_flat_buttons_opt_out(self):
         qss = theme.button_emboss_qss(QColor("#808080"))