Builds polish + attach reconnect

[blakebauman]

Summary

• Attach reliability: POST /api/docker/reconnect rebuilds the Docker SDK client; status includes live Ping errors + active context/host
• Dashboard offline empty state: Retry connection + Open Settings (no false “auto reconnect” copy)
• Settings Diagnose/Engine: Reconnect buttons; Docker dock chip goes to Settings when offline (soft monotone when sidecar is up)
• App keeps probing sidecar health/URL after forced ready
• Builds: offline banner + retry, quieter Hub rows, pull progress sheet, accent Build

Test plan

• Stop Docker → Dashboard shows Retry; Reconnect after starting engine succeeds
• Settings → Diagnose Reconnect + Engine Reconnect when offline
• Dock Docker chip offline → Settings; tip shows Ping error
• Builds: offline banner; with Docker up, Build / Search / Pull sheets work
• bun run --filter @deckhand/app build and go build ./... in sidecar

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