docs: reframe README opener around the human+agent audience (#90)

The previous opener led with what the harness is (a coding harness for
Python+React) and folded the audience into a trailing clause. The new
opener leads with who it's for — teams pairing AI agents with human
engineers — and keeps the mechanism punchline ("every gate enforced
mechanically in CI, not by discipline") that makes the harness story
distinctive.

Wording matches the repo's GitHub description for consistency between
the two surfaces.

Closes #90

Author: constk

README.md

@@ -8,7 +8,7 @@
 [![React 19.2](https://img.shields.io/badge/react-19.2-61dafb.svg)](https://react.dev/)
 [![Coverage 98%](https://img.shields.io/badge/coverage-98%25-brightgreen.svg)](docs/HARNESS.md)
 
-> A production-quality coding harness for Python (FastAPI) + Vite/React/TypeScript projects. Designed for LLM-driven development: every gate — lint, types, architecture, security, eval — is enforced mechanically so code quality stays consistent across many human and AI contributors.
+> Production-grade SDLC scaffold for teams pairing AI agents with human engineers — keeping quality consistent regardless of who's at the keyboard. Python (FastAPI) + Vite/React/TypeScript, with every gate (lint, types, architecture, security, eval) enforced mechanically in CI, not by discipline.
 
 ## What ships