[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.

cockatrice/src/interface/theme_manager.cpp

@@ -681,6 +681,7 @@ QFont ThemeManager::cardTextFont() const
     }
     QFont serifFont(QStringLiteral("Serif"));
     serifFont.setStyleHint(QFont::Serif);
+    serifFont.setPointSize(12);
     return serifFont;
 }
 
@@ -702,6 +703,29 @@ QFont ThemeManager::defaultAppFont(AppFont::Role /*role*/) const
     return defaultFont;
 }
 
+int ThemeManager::cardTextMaxSize() const
+{
+    if (currentFonts.cardTextMaxSize > 0) {
+        return currentFonts.cardTextMaxSize;
+    }
+    const auto it = currentFonts.fonts.constFind(AppFont::CardText);
+    if (it != currentFonts.fonts.constEnd()) {
+        const int size = it.value().pointSize();
+        if (size > 0) {
+            return size;
+        }
+    }
+    return 12;
+}
+
+int ThemeManager::cardTextMinSize() const
+{
+    if (currentFonts.cardTextMinSize > 0) {
+        return currentFonts.cardTextMinSize;
+    }
+    return 1;
+}
+
 void ThemeManager::themeChangedSlot()
 {
     QString themeName = SettingsCache::instance().getThemeName();