fix: draw classroom icons at the display's real pixel density

Icons went soft under UI_SCALE while the clock text beside them stayed
sharp, which is visible on a 24" monitor even if it hides on a TV.

new_from_file_at_scale rasterises an SVG at its *logical* size. The
artwork is vector, but by the time sway scaled the session it was
already a fixed raster, and the compositor enlarged that. Text never had
the problem because GTK draws it at the real density.

GTK 3 has no fractional scaling, so sway advertises the ceiling integer
scale and scales the finished buffer down. Measured under sway: scale
factor 1 at output scale 1.0, and 2 at 1.25, 1.5 and 2.0. So each icon
is now rasterised at size x scale_factor physical pixels and handed to
GTK as a cairo surface carrying that device scale. The icon lands at the
real density; its logical size, and the whole dock layout, is unchanged.

Icons redraw on notify::scale-factor as well as at realize, since the
scale factor is not known until a widget is on a display and changes if
UI_SCALE is changed under a running session.

Browser, DVD, LIVE and all six DVD control icons go through it, in a
shared module so the dock and the DVD session cannot diverge. The
throbber is drawn rather than loaded and had the same flaw, so it draws
on a device-scaled surface too rather than being the one soft thing left
in a sharp dock.

The artwork is untouched. Verified by rendering the dock under sway at
1.0, 1.25, 1.5 and 2.0 against the previous build: apparent icon size is
identical at every scale (28, 35, 42, 56 px), 1.0 is unchanged
pixel-for-pixel, and peak edge contrast on the Chrome icon goes from 60
to 99 at 1.25, 49 to 83 at 1.5, and 37 to 82 at 2.0 out of 255. The DVD
control bar was checked the same way.

Also records that Wonder Ink session-only cookies are confirmed working
on the endpoint, which settles the question 0.1.34 shipped as unverified
and tells us the session is in cookies rather than localStorage.

Co-Authored-By: Claude Opus 5 <[email protected]>

scripts/classroom-dvd-session

@@ -33,10 +33,9 @@ import gi
 
 gi.require_version("Gtk", "3.0")
 gi.require_version("Gdk", "3.0")
-gi.require_version("GdkPixbuf", "2.0")
 gi.require_version("GtkLayerShell", "0.1")
 
-from gi.repository import Gdk, GdkPixbuf, GLib, Gtk, GtkLayerShell
+from gi.repository import Gdk, GLib, Gtk, GtkLayerShell
 
 sys.path.insert(0, "/usr/local/lib/ekklesia-classroom")
 sys.path.insert(
@@ -49,6 +48,7 @@ import classroom_style as style  # noqa: E402
 import classroom_sway as sway  # noqa: E402
 import classroom_vlc as vlc  # noqa: E402
 from classroom_config import SHELL_SCALE, read_device_config, scaled  # noqa: E402
+from classroom_icons import ScalableIcon  # noqa: E402
 
 # Input shaping needs pycairo. Without it the bar still works, it just
 # takes pointer events across its whole strip instead of only where it
@@ -141,12 +141,8 @@ window#classroom-dvd-bar {{
 
 
 def icon(filename, size):
-    path = ICON_DIR / filename
-
-    if not path.exists():
-        return None
-
-    return GdkPixbuf.Pixbuf.new_from_file_at_scale(str(path), size, size, True)
+    """A control bar icon, drawn at the display's real pixel density."""
+    return ScalableIcon(filename, size, ICON_DIR)
 
 
 def free_port():
@@ -324,8 +320,7 @@ class ControlBar(Gtk.Window):
             button.set_relief(Gtk.ReliefStyle.NONE)
             button.get_style_context().add_class("dock-button")
 
-            pixbuf = icon(filename, scaled(ICON_SIZE, scale))
-            image = Gtk.Image.new_from_pixbuf(pixbuf) if pixbuf else Gtk.Image()
+            image = icon(filename, scaled(ICON_SIZE, scale))
 
             self.images[name] = image
             button.add(image)
@@ -446,13 +441,7 @@ class ControlBar(Gtk.Window):
         if image is None:
             return
 
-        pixbuf = icon(
-            "media-pause.svg" if playing else "media-play.svg",
-            scaled(ICON_SIZE, self.scale),
-        )
-
-        if pixbuf is not None:
-            image.set_from_pixbuf(pixbuf)
+        image.set_icon("media-pause.svg" if playing else "media-play.svg")
 
 
 class DvdSession: