Fix Decodex app running task stream

[yvette-carlisle]

Summary

• replace the app running-task stream with a pure WebSocket reader that handles large dashboard snapshots
• keep one long-lived stream with reconnect/backoff and no panel-triggered reconnect loop
• show active runs globally, tick child-agent elapsed locally, and label stopped active runs as idle instead of normal running work

Validation

• swift test --package-path apps/decodex-app
• git diff --check
• cargo make test-decodex-app-stage
• launched Decodex.app and verified one ESTABLISHED WS connection to 127.0.0.1:8192