addyosmani/agent-skills ? reverse-engineered prompt

I want to build a set of "skills" for an AI coding agent to make it work like a senior software engineer. The main idea is to give the agent a structured workflow that follows best practices for building real applications.

Let's organize it around the main phases of development: defining the project, planning the tasks, building the code, testing, reviewing, and shipping. For each phase, there should be simple slash commands like /spec, /plan, or /build to guide the agent.

Underneath these commands, we'll need around 20 specific skills. These skills will be detailed instructions in markdown files. They should cover important engineering principles like test-driven development, creating good user interfaces with accessibility, secure API design, and how to write clean, simple code. The system should be packaged so it can be easily plugged into coding assistants like Cursor and Claude.