fix(shutdown): stabilize drain teardown

[corylanou]

Summary

• publish and latch draining telemetry before potentially blocked orchestrator work
• keep health and state endpoints responsive during drain without store or project enrichment
• preserve forced and timed-out shutdown results over cancellation cleanup noise while reaping owned worker groups under one deadline
• route second signal and TUI interrupts through the shutdown state machine with a bounded OS fallback

Fixes #1484

UI Surface Contract

• N/A; this change does not alter a high-impact UI surface, layout, density, first viewport, or responsive visibility.
• This PR does not add persistent top-of-screen messaging.
• No visual changes to primary operator screens.

Test Plan

• go test -race ./cmd/detent ./internal/cli ./internal/tui ./internal/web -count=1
• make check

[chatgpt-codex-connector]

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