Introduce architettura multi-sport con catalogo, engine scoring e overlay.

Catalogo sport in YAML, board implicito, engine per volley/basket/timed/racket/timer/generic, regia e app Android allineate.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/domain/sports/overlay_kind.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module Sports
+  class OverlayKind
+    ALL = %w[none timer volley basket timed racket].freeze
+
+    def self.valid?(value)
+      ALL.include?(value.to_s)
+    end
+  end
+end