Description

Decouple the simulation engine from the global window scope, enabling testability in Node/Vitest environments.

Acceptance Criteria

• #1 Convert PhxBattle to an ES Module export.
• #2 Update site imports to use the new module.
• #3 Maintain global window scope for existing legacy calculator pages.

Definition of Done

• #1 The a11y is run agains the site and all claims are verified against the official rules and guidlines for Phalanx Duel