Preserve and expose host/session recovery status in fleet APIs #216

Goal

Add host and session recovery detail to the aggregated API and render it without implying a healthy attachment.

Scope

• Preserve managed tmux sessions across expected process and network interruptions.
• Never duplicate a session, replay a control action, or silently discard a pending approval.

Acceptance

• Add host and session recovery detail to the aggregated API and render it without implying a healthy attachment.
• Cover restart, disconnect, timeout, and duplicate-message paths.
• Export explicit recovery state to the fleet API.

Verification

• go test -race ./internal/web ./internal/daemon && npm --prefix frontend test

Dependencies

#205, #211, #212, #214