Senior Python Full Stack Developer (FastAPI + PostgreSQL + Windows Server) for Existing ERP Project

About the Project We are developing an internal ERP system for a California structural engineering firm. The UI and business workflow have already been designed and frozen. This is NOT a greenfield project. The system already has well-defined business requirements, and we are looking for an experienced developer to continue development using the existing architecture without redesigning the user interface. This is expected to become a long-term project. Important Requirement The UI is frozen. The developer must not redesign: Layout Navigation Menus Tabs Button locations Existing workflow The goal is to improve functionality while preserving the current user experience. Tech Stack Backend Python 3.12 FastAPI SQLAlchemy Alembic PostgreSQL 16 Frontend Existing HTML/CSS/JavaScript (Vue experience is a plus) Deployment Windows Server 2019 Windows Service IIS or Nginx Reverse Proxy Cloudflare Tunnel Version Control Git GitHub Current Modules The ERP already contains the following business modules: Dashboard User Management Role & Permission Management Client Management CRM Project Management Proposal Proposal Fee Schedule Invoice Observation Invoice Load Sheet Cover Sheet Reports Settings Excel Import / Export PDF Printing Most UI screens already exist. The work mainly focuses on backend implementation and business logic. What We Expect We are looking for a long-term developer. The project will continue for many months. We prefer someone who can: write clean code follow an existing architecture avoid unnecessary redesign communicate well use Git professionally Coding Rules These rules are mandatory. DO Preserve the current UI Write clean and modular code Keep backward compatibility Add database migrations Create reusable APIs Document important changes DO NOT Redesign the UI Rename existing business logic Break existing features Rewrite modules unnecessarily Deliverables Every sprint should include: Source Code Git Commit Database Migration Documentation Test Report As part of your proposal, please briefly describe how you would implement a production-ready FastAPI + PostgreSQL architecture with Alembic migrations, role-based permissions, and a frozen UI. Also include links to one or two ERP/CRM or similar business applications you have personally developed.