Fix Claude CLI Execution on Windows for test_anthropic_api_key_handling

[yeabwang]

Issue: Test test_anthropic_api_key_handling fails on Windows with "Claude CLI not installed" because subprocess.run(["claude", ...]) doesn’t handle claude.ps1.

Steps to Reproduce:

1. Install Claude CLI (npm install -g @anthropic-ai/claude-code).

2. Run pytest claudecode/test_integration.py::TestEnvironmentSetup::test_anthropic_api_key_handling.

3. Error: Failed: Claude CLI not installed.

Root Cause: SimpleClaudeRunner uses subprocess.run without handling PowerShell scripts.

Environment: Windows 11, Claude CLI 1.0.71, Node.js 22.17.0, npm 10.9.2.