[Fonts] Keep CardText call sites on the app font and fix px sizes

- CardText's unset fallback is qApp->font() again: only the three counter
  painters (paintNumberEllipse, GeneralCounter, PlayerCounter) were Serif
  before the role existed, and they now ask for it through
  ThemeManager::cardTextFont(). Card names, player names, counters, the
  overlay, the Archidekt and EDHREC labels and the completer delegate keep the
  app font they used before.
- Use setPixelSize for the EDHREC card name (20px) and commander name (28px)
  and details (16px) sizes: the stylesheets said px, and setPointSize made
  them about a third larger.

cockatrice/src/interface/theme_manager.h

@@ -156,6 +156,9 @@ public:
     QFont appFont(AppFont::Role role) const;
     /** @brief Whether the active theme defines this role in fonts.toml. */
     bool hasAppFont(AppFont::Role role) const;
+    /** @brief The CardText role with its historical Serif fallback. Used by the
+     *         counter painters, which were Serif before the role existed. */
+    QFont cardTextFont() const;
     /** @brief Resolves an application font role against the startup font only,
      *         ignoring any previewed config in currentFonts. Editors that show
      *         "what this role resolves to" must use this, because appFont()