[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/sort_arrow_down.svg

@@ -1 +1,7 @@
-<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="M278.6 438.6L182.6 534.6C170.1 547.1 149.8 547.1 137.3 534.6L41.3 438.6C28.8 426.1 28.8 405.8 41.3 393.3C53.8 380.8 74.1 380.8 86.6 393.3L128 434.7L128 128C128 110.3 142.3 96 160 96C177.7 96 192 110.3 192 128L192 434.7L233.4 393.3C245.9 380.8 266.2 380.8 278.7 393.3C291.2 405.8 291.2 426.1 278.7 438.6zM352 544C334.3 544 320 529.7 320 512C320 494.3 334.3 480 352 480L384 480C401.7 480 416 494.3 416 512C416 529.7 401.7 544 384 544L352 544zM352 416C334.3 416 320 401.7 320 384C320 366.3 334.3 352 352 352L448 352C465.7 352 480 366.3 480 384C480 401.7 465.7 416 448 416L352 416zM352 288C334.3 288 320 273.7 320 256C320 238.3 334.3 224 352 224L512 224C529.7 224 544 238.3 544 256C544 273.7 529.7 288 512 288L352 288zM352 160C334.3 160 320 145.7 320 128C320 110.3 334.3 96 352 96L576 96C593.7 96 608 110.3 608 128C608 145.7 593.7 160 576 160L352 160z"/></svg>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+<path d="M4 6h10"/>
+  <path d="M4 12h7"/>
+  <path d="M4 18h4"/>
+  <path d="M18 8v10"/>
+  <path d="M15 15l3 3 3-3"/>
+</svg>