[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.

tests/settings/settings_defaults_test.cpp

@@ -461,19 +461,6 @@ TEST_F(SettingsDefaultsTest, Appearance_StyleUserList_Default)
     ASSERT_EQ(s.getStyleUserList(), true);
 }
 
-TEST_F(SettingsDefaultsTest, Appearance_MaxFontSize_Default)
-{
-    AppearanceSettings s(settingsPath, nullptr);
-    ASSERT_EQ(s.getMaxFontSize(), 12);
-}
-
-TEST_F(SettingsDefaultsTest, Appearance_MaxFontSize_SetAndGet)
-{
-    AppearanceSettings s(settingsPath, nullptr);
-    s.setMaxFontSize(14);
-    ASSERT_EQ(s.getMaxFontSize(), 14);
-}
-
 TEST_F(SettingsDefaultsTest, Appearance_HomeTabBackgroundSource_Default)
 {
     AppearanceSettings s(settingsPath, nullptr);