feat(monitor): stream session detail updates while viewing

[moltar-bot]

Summary

Adds near real-time streaming behavior to the Agent Monitor detail panel while a session is open.

When you click into a session on the Monitor page, the panel now auto-refreshes in place:

• Regular sessions: every 2s
• Cron sessions: every 5s

This gives a live, "streaming" feel without requiring a new backend SSE/WebSocket endpoint.

What changed

• Updated SessionDetailPanel to support silent background refreshes while open
• Added refresh timers + in-flight request guard to prevent overlapping fetches
• Kept initial load behavior the same (loading spinner on first open)
• Silent polls update messages only when fingerprint changes (reduces unnecessary re-renders)
• Cron panels also refresh latest run details and messages while open

Validation

• npm run -w ./web lint

[Copilot]

Pull request overview

Adds near real-time polling to the Monitor session detail drawer so that an open session view stays up-to-date without requiring SSE/WebSockets.

Changes:

• Introduces periodic background refresh while the detail panel is open (2s for regular sessions, 5s for cron sessions).
• Adds an in-flight request guard and “silent refresh” mode to avoid showing the loading spinner on every poll.
• Avoids unnecessary re-renders by only updating messages when a simple fingerprint changes.

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