Add auto-refresh polling for debug view

[yazinsai]

Summary

• Adds automatic polling (every 3 seconds) to the debug view when active
• Removes the need to manually click refresh button to see updated debug messages
• Implements the same polling pattern used for logs and nodes views

Changes

• Added startDebugPolling() and stopDebugPolling() functions in app-polling.ts
• Updated lifecycle handlers to start/stop polling on connection/disconnection
• Updated tab switching logic to start/stop polling when entering/leaving debug tab
• Added debugPollInterval property to track the polling state

Test plan

• Navigate to /chat (debug tab) in the gateway UI
• Verify debug information (status, health, models, heartbeat) refreshes automatically every 3 seconds
• Verify no manual refresh button clicking is needed
• Switch to other tabs and verify polling stops
• Switch back to debug tab and verify polling resumes

[steipete]

Landed via temp rebase onto main.\n\n- Gate: pnpm lint && pnpm build && pnpm test\n- Land commit: 2f47b3f\n- Merge commit: 2d1d793\n\nThanks @yazinsai!