docs: enhance README header with badges, tagline, and SEO-friendly intro

Boost discoverability without changing any of the install / configuration
documentation that users rely on day-to-day:

- Add a one-line tagline above the description so the value prop ("drive
  Claude Code / Gemini CLI / Codex CLI from your phone, code stays on
  your machine") is visible in GitHub list previews and trending cards.
- Add 5 shields.io badges (release, license, Go reference, Go report card,
  stars) — these are the standard cues GitHub users scan for "is this
  repo alive and trustworthy" before reading the rest of the README.
- Bold the runtime names (Claude Code, Gemini CLI, Codex CLI) in the
  intro paragraph so the brand keywords stand out for both human readers
  and search engines.
- Leave a TODO comment for a future docs/demo.gif — visual assets are a
  major GitHub trending and Hacker News thumbnail signal but require
  separate recording work.

Everything below "## How it works" is unchanged.

Author: cici

README.md

@@ -1,6 +1,21 @@
 # codewithphone
 
-Local AI agent runtime for [CodeWithPhone](https://codewithphone.com). Connects your machine to the CodeWithPhone platform so you can run AI coding tasks using Claude, Gemini, and Codex CLIs directly on your local environment.
+> AI coding agent runtime — drive Claude Code, Gemini CLI, and Codex CLI from
+> your phone or browser. Code stays on your machine; the agent runs locally.
+
+[![Release](https://img.shields.io/github/v/release/shotforward/codewithphone)](https://github.com/shotforward/codewithphone/releases)
+[![License](https://img.shields.io/github/license/shotforward/codewithphone)](LICENSE)
+[![Go Reference](https://pkg.go.dev/badge/github.com/shotforward/codewithphone.svg)](https://pkg.go.dev/github.com/shotforward/codewithphone)
+[![Go Report Card](https://goreportcard.com/badge/github.com/shotforward/codewithphone)](https://goreportcard.com/report/github.com/shotforward/codewithphone)
+[![Stars](https://img.shields.io/github/stars/shotforward/codewithphone?style=social)](https://github.com/shotforward/codewithphone/stargazers)
+
+`codewithphone` is the local agent runtime for [CodeWithPhone](https://codewithphone.com).
+It connects your machine to the CodeWithPhone platform so you can run AI coding
+tasks using **Claude Code**, **Gemini CLI**, and **Codex CLI** directly on your
+local environment — supervised from your phone, browser, or wherever you are.
+
+<!-- TODO: add a 30-second demo GIF at docs/demo.gif and reference it here.
+     High-impact for GitHub trending placement and Hacker News thumbnails. -->
 
 ## How it works