[Icons] Add Hidden and Marked semantic color families

Two game concepts had no hue of their own. Hidden information (a face-down
play, peeking at a card face) now has violet, and the marks a player leaves on a
card (annotation, draw arrow) now share amber instead of splitting blue and red
for the same job.

Both families follow the existing three-level 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 and keep the saturation ordering the emphasis tests assert; the hue
tests pin violet's blue-red-green dominance and amber's red-green-blue one, and
every preview sheet now renders the two families.

The hover panel grid preview is added alongside: it renders the real pages
(section headers, two-column cells, glyph over label) so the whole map can be
judged at once instead of glyph by glyph.

tests/theme_migration/icon_tint_preview_test.cpp

@@ -103,6 +103,8 @@ TEST(IconTintPreview, WritesOneSheetPerShippedTheme)
         {"Positive", AppColor::Positive, {"increment", "ready_start", "arrow_up"}},
         {"Negative", AppColor::Negative, {"decrement", "not_ready_start", "remove_row"}},
         {"Informational", AppColor::Informational, {"arrow_right", "view", "arrow_to_top"}},
+        {"Hidden", AppColor::Hidden, {"view", "arrow_right", "swap"}},
+        {"Marked", AppColor::Marked, {"pencil", "share", "pin"}},
     };
     const QStringList themes = {
         QStringLiteral("Fabric"), QStringLiteral("Fusion"),       QStringLiteral("Leather"),