I’ve built the first version of a billing web application on Replit AI and now need a skilled developer to take it to the next stage. The main focus is to extend the current codebase, give it a clearer structure, and plug in three new pieces of functionality: • Invoice generation – must handle auto-calculations, apply taxes automatically, and let me swap or tweak invoice templates without touching the code. • Expense tracking – lay the groundwork for recording day-to-day business costs so they can be tied back to each invoice or customer. • Analytics & reporting – add a basic model that summarises revenue vs. expenses and outputs easy-to-read charts or tables. Your task is to refactor the existing project into clean modules, wire up these new models, and make sure everything still runs smoothly inside the Replit environment. I’m happy with a straightforward MVP: robust database schemas, simple forms or APIs, and clear documentation so I can keep building later. If you’ve used Replit AI before and can move fast on Python/Flask (or a comparable stack), I’d love to see how you’d approach this.