[Fonts] Retire max font size setting into theme CardText min/max range

The per-card text size lives in the theme now, so a theme can pick the size
it was designed for instead of every user overriding it globally.

- CardText stores family + max point size; CardTextMinSize stores the
  overlay shrink-to-fit floor (omitted from fonts.toml when 1).
- ThemeManager::cardTextMaxSize()/cardTextMinSize() resolve the range with
  the retired defaults (12 max, 1 min), and cardTextMaxSize() falls back to
  the CardText role size that #7541 made live.
- The overlay widget starts at the explicit size when one is set (deck
  preview), else the theme max, and shrinks down to the theme floor.
- The appearance page's "Maximum font size" spin is gone; the range is
  edited in the theme's font grid, whose min/max spins now keep the saved
  range consistent with each other.
- Migration: appearance/maxFontSize is seeded into every user theme folder
  and into the active theme's folder (created when the theme is a shipped
  one that only exists in the system directory). The retired
  game/maxfontsize -> appearance/maxFontSize mapping stays, so users still
  on global.ini keep their value through the chain.

libcockatrice_settings/libcockatrice/settings/appearance_settings.cpp

@@ -33,16 +33,6 @@ void AppearanceSettings::setStyleUserList(bool _styleUserList)
     emit styleUserListChanged();
 }
 
-int AppearanceSettings::getMaxFontSize() const
-{
-    return getValue("maxFontSize", QString(), QString(), 12).toInt();
-}
-
-void AppearanceSettings::setMaxFontSize(int _max)
-{
-    setValue(_max, "maxFontSize");
-}
-
 QString AppearanceSettings::getHomeTabBackgroundSource() const
 {
     return getValue("homeTabBackgroundSource", QString(), QString(), "themed").toString();