fix: Set machines to active when receiving machine-alive events

[taranasus]

Summary

• Fixed bug where machines never became active after sending machine-alive events

Problem

The flushPendingUpdates() method in sessionCache.ts was updating lastActiveAt for machines but not setting active: true, unlike the session update logic which correctly sets both.

This caused machines to:

1. Be created with active: false (default)
2. Never become active despite sending machine-alive events
3. Be invisible in the mobile app's machine list (which filters to only show active: true machines)

Fix

Added active: true to the machine update data, matching the session update behavior:

- data: { lastActiveAt: new Date(update.timestamp) }
+ data: { lastActiveAt: new Date(update.timestamp), active: true }

Testing

Verified the fix by deploying to a self-hosted instance. Machines now correctly appear in the mobile app after sending alive events.