[Icons] Add a Movement semantic color family

A card changing position inside the library is neither a gain, a loss nor
information, so it had no hue. Movement names it with teal and covers the three
library placements (top, bottom, X from top).

It follows the existing ladder: authored roles per theme, scheme defaults
otherwise, an emphasis mapping, palette-editor rows and generator seeding. The
defaults clear the 4.5:1 floor on the representative platform surfaces, keep
strong > base > soft saturation, and keep green > blue > red so teal cannot be
mistaken for the green gain family.

tests/theme_migration/icon_tint_preview_test.cpp

@@ -105,6 +105,7 @@ TEST(IconTintPreview, WritesOneSheetPerShippedTheme)
         {"Informational", AppColor::Informational, {"arrow_right", "view", "arrow_to_top"}},
         {"Hidden", AppColor::Hidden, {"view", "arrow_right", "swap"}},
         {"Marked", AppColor::Marked, {"pencil", "share", "pin"}},
+        {"Movement", AppColor::Movement, {"arrow_to_top", "arrow_to_bottom", "arrow_down"}},
     };
     const QStringList themes = {
         QStringLiteral("Fabric"), QStringLiteral("Fusion"),       QStringLiteral("Leather"),