Refactoring & Final Application Logic

You have built the calculator feature by feature. Before calling the project finished, take one pass through the logic.

The goal is not to rewrite everything. It is to make responsibilities clear:

• calculator.js owns calculator state and calculations.
• ui.js connects user actions to calculator methods and updates the display.
• history.js manages history rendering and persistence.

Then you will test the complete workflow from a fresh application state.