Push Notifications for All Session Completions

[dzianisv]

Problem

Push notifications only work for sessions that are currently open in the UI. Users want to be notified when ANY session completes, even if not viewing it.

Solution

Implement global push notifications for all session completions with click-to-navigate functionality.

Acceptance Criteria

• Push notifications sent when any session becomes idle (completes processing)
• Notification shows session title and repository name
• Clicking notification navigates directly to that session
• Works even when app is not focused or tab is not active
• Respects user's notification settings (can be disabled)
• Works across all repositories/sessions, not just the viewed one

Technical Notes

• Backend already has push notification service (services/push.ts)
• Need to ensure SSE events trigger push for all sessions, not just active ones
• Service worker needs to handle notification click and navigate properly

[chriswritescode-dev]

@ #110