docs: update project tagline to The team harness for AI agents (merge request !180)

Squash merge branch 'worktree-update-tagline' into 'master'
## Summary

- 更新项目 tagline 为 "The team harness for AI agents"
- 副标题明确两大核心能力：(1) 跨 AI Agent 同步 skills/rules/docs；(2) 构建团队共享知识库
- 涉及文件：README.md, README.en.md, package.json, src/index.ts

## Test plan

- [x] grep team harness 命中 4 个文件
- [x] 旧 tagline 不再出现
- [x] npx tsc --noEmit 通过

README.en.md

@@ -1,4 +1,4 @@
-# TeamAI — Git-native Team AI Experience Sharing
+# TeamAI — The team harness for AI agents
 
 > [English](README.en.md) | [简体中文](README.md)
 

README.md

@@ -1,4 +1,4 @@
-# TeamAI — 基于 Git 的团队 AI 经验共享工具
+# TeamAI — The team harness for AI agents
 
 > [English](README.en.md) | [简体中文](README.md)
 

package.json

@@ -1,7 +1,7 @@
 {
   "name": "teamai-cli",
   "version": "0.16.2",
-  "description": "TeamAI — team AI experience sharing framework (skills, rules, docs, env sync across Claude Code, Cursor, Codex, etc.)",
+  "description": "TeamAI — the team harness for AI agents (skill sync + shared knowledge base, powered by Git)",
   "type": "module",
   "bin": {
     "teamai": "./dist/index.js"

src/index.ts

@@ -10,7 +10,7 @@ const program = new Command();
 
 program
   .name('teamai')
-  .description('TeamAI — 团队 AI 经验共享框架')
+  .description('TeamAI — The team harness for AI agents')
   .version(version)
   .option('--dry-run', 'Preview mode, no changes made')
   .option('-v, --verbose', 'Verbose output')