enhancement : Add onboarding validation command (webwright doctor)

从 @app.command() 所示的 CLI 集成点开始，检查提议的 webwright/run/doctor.py 模块和 CHECKS 结构。实现所列出的环境、Playwright、配置和运行时检查，使 webwright doctor 能够报告 pass/fail 结果，并针对设置问题提供可执行的修复措施。

Add webwright doctor onboarding validation command

Summary

Add a webwright doctor CLI command that validates local environment setup and provides actionable fixes for common onboarding/runtime issues.

---

Current State

Webwright setup currently requires multiple manual steps:

• Python environment setup
• Playwright installation
• Chromium browser installation
• Claude/Codex plugin setup
• API key configuration
• Browser runtime validation

When something is misconfigured, failures often happen later during runtime with limited debugging guidance.

Examples:

• Missing Chromium binaries
• Playwright not installed
• Missing API keys
• Plugin manifest/configuration issues
• Screenshot permission failures

This creates onboarding friction for new contributors and users.

---

Desired State

Provide a command:

webwright doctor

that validates the local environment before runtime.

Example output:

Webwright Doctor

[PASS] Python 3.11 detected
[PASS] playwright installed
[FAIL] Chromium missing
       Fix: playwright install chromium

[PASS] OPENAI_API_KEY detected
[FAIL] Claude plugin manifest missing

4/6 checks passed

---

Proposed Checks

Environment

• Python version compatibility
• Required package availability
• Writable directories

Playwright

• Playwright installation
• Chromium/browser availability
• Headless launch validation

Configuration

• API key detection
• Plugin manifest detection
• Environment variable validation

Runtime Validation

• Launch browser
• Open simple webpage
• Capture screenshot successfully

---

Proposed Implementation

New Module

webwright/run/doctor.py

CLI Integration

@app.command()
def doctor():
    run_doctor()

Suggested Structure

CHECKS = [
    check_python,
    check_playwright,
    check_chromium,
    check_api_keys,
    check_plugins,
    check_screenshot,
]

Optional Enhancements

• --verbose
• --fix
• JSON output mode
• CI compatibility

---

Benefits

• Easier onboarding
• Better contributor experience
• Faster debugging
• Fewer duplicate setup issues
• Reduced maintainer support burden

---

Scope

This should be relatively self-contained and beginner/intermediate contributor friendly.