Improve Electron update CTA flow

[ignaciojimenezr]

This PR makes the Electron app show the update button earlier.

Before this change, the button only appeared after the update had already been downloaded.
Now, the app can show the button as soon as it knows a newer version exists.

It also keeps the existing restart flow:

• if the update is already downloaded, clicking the button restarts into the new version
• if the update is still in progress, the app remembers the user's intent and installs once the download finishes

Why this changed

The old behavior was too late.
Users could be on an old version and see nothing, even though an update was already available.

Extra fixes included

• expanded the Vite fs allow-list so electron:dev boots correctly

Checks run

• desktop updater tests
• client hook tests
• server test for the sandbox proxy route
• full npm run build

[chelojimenez]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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