[Icons] Migrate UI glyphs to palette-token SVGs

Runtime inversion is not a theming system: it rotates hue, breaks duotone art
and mishandles alpha, and a QPixmap snapshot cannot follow a palette change.
Redraw the top-level UI glyph set on a 24x24 grid with `currentColor` as the
paint token, drop Inkscape/Sodipodi cruft, and delete the icons whose metaphor
was duplicated (cogwheel/gear -> settings, scale_balanced -> scales,
update.png -> reload).

Load the glyphs through `loadThemedIcon` so the engine resolves the token from
the palette on every request, and let `themePixmap` use the same resolution for
one-shot pixmaps. `loadColorAdjustedPixmap` is gone; every caller now keeps a
QIcon, which `SettingsButtonWidget::setButtonIcon` accepts instead of a QPixmap.

Content art (mana, counters, countries) keeps its authored colors.

Add a render test covering aspect ratio, palette flips, icon modes and
high-DPI pixmaps.

cockatrice/resources/icons/circle_half_stroke.svg

@@ -1 +1,4 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 640 640"><!--!Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free Copyright 2026 Fonticons, Inc.--><path d="M512 320C512 214 426 128 320 128L320 512C426 512 512 426 512 320zM64 320C64 178.6 178.6 64 320 64C461.4 64 576 178.6 576 320C576 461.4 461.4 576 320 576C178.6 576 64 461.4 64 320z"/></svg>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
+  <circle cx="12" cy="12" r="9" fill="none" stroke="currentColor" stroke-width="2"/>
+  <path d="M12 3a9 9 0 0 1 0 18z" fill="currentColor"/>
+</svg>