[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.h

@@ -169,6 +169,11 @@ public:
      *         "what this role resolves to" must use this, because appFont()
      *         reflects a live preview while the editor is open. */
     QFont defaultAppFont(AppFont::Role role) const;
+    /** @brief CardText max size: stored CardTextMaxSize, else the CardText
+     *         point size, else 12. */
+    int cardTextMaxSize() const;
+    /** @brief CardText shrink-to-fit floor: stored CardTextMinSize, else 1. */
+    int cardTextMinSize() const;
 
     QBrush &getBgBrush(Role zone);
     QBrush getExtraBgBrush(Role zone, int zoneId = 0);