[Phase 1b] Implement prompt interception in oop-host.ps1

[usepowershell]

Part of #98

Implement prompt interception in the out-of-process host and emit structured prompt metadata.

Subtasks

• Detect prompt events in host flow
• Emit prompt metadata (type/message/promptId)
• Accept retry payload and inject response on re-run
• Ensure no deadlocks on stdio channel
• Add diagnostics/logging
• Tests

Effort: 1-2 weeks