docs: 文档审查修正 + README 增加 npm 安装说明

[zx06]

修正问题:

1. README.md: 增加 npm install -g xsql-cli 安装方式
2. README.md: 修正 proxy 命令示例参数顺序，与 cli-spec 保持一致
3. README.md: spec 命令描述补充 --format yaml 支持说明
4. npm/xsql/README.md: 修正用法示例，使用 -p profile 而非不存在的 --dsn
5. docs/architecture.md: 补充遗漏的 /internal/proxy 目录
6. docs/dev.md: 补充 proxy/ 和 tests/e2e/ 目录
7. docs/testing.md: 更新 E2E 测试目录结构（补充 7 个测试文件）
8. internal/app/app.go: 移除 spec 中不存在的 --read-only flag

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.02%. Comparing base (f7f4895) to head (3b5308a).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
- Coverage   79.03%   79.02%   -0.02%     
==========================================
  Files          32       32              
  Lines        1865     1864       -1     
==========================================
- Hits         1474     1473       -1     
  Misses        326      326              
  Partials       65       65              

Flag	Coverage Δ
e2e	48.64% <ø> (ø)
integration	48.64% <ø> (ø)
unittests	78.75% <ø> (-0.02%)	⬇️

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