[Phase 1a] Integration tests for Read-Host, Get-Credential, and device code

[usepowershell]

Part of #98

Write end-to-end tests for prompt scenarios.

Test Scenarios

• Read-Host with text input
• Get-Credential with username/password
• Device code flow (Connect-AzAccount simulation)
• Confirmation prompt (-Confirm:$true)
• Multiple prompts in single command
• Timeout on no response
• Concurrent requests with different prompts
• Retry with same snapshot
• Retry with invalid/expired snapshot

Effort: 1 week