[Fonts] Keep ChatView on the app font and share the report log font

- ChatLog's unset fallback is qApp->font() again: ChatView never set a font
  before the role existed, so an unset role must not switch chat and the game
  log to monospace at the system GeneralFont size.
- Move the monospace fallback the report dialogs used before into
  report_utils::reportLogFont(), which returns the theme's ChatLog role when it
  is set and the old monospace otherwise. tab_report, dlg_my_reports and
  dlg_report_user now share it, so they cannot drift and they honour a themed
  size instead of overriding it.

cockatrice/src/interface/theme_manager.h

@@ -154,6 +154,8 @@ public:
      *         ChatLog, serif basis for CardText, the application font for the
      *         remaining roles). */
     QFont appFont(AppFont::Role role) const;
+    /** @brief Whether the active theme defines this role in fonts.toml. */
+    bool hasAppFont(AppFont::Role role) 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()