[Fix] Surface worker provisioning progress and failures on Settings > Sandboxes

[mrubens]

Problem

Settings → Sandboxes already receives the detached worker base-image provisioning state and polls while a run is building, but presents none of it:

• While a run is in flight the save button shows a generic "Saving..." spinner (the setup wizard shows "Provisioning..." for the same state), so a multi-minute Daytona snapshot registration looks like a hung save.
• A failed run is never displayed. Real incident: saving a Daytona API key that lacked snapshot permissions returned "saved" in the UI while the registration died server-side with Access denied — the only evidence was in the web service logs.

Change

ComputeProviderSection now matches the wizard's presentation:

• Button reads "Provisioning..." while provisioning.status === 'building', with a note that the run can take a few minutes.
• A failed run renders its persisted error in a destructive alert (falling back to generic copy when no error was recorded), and the button reads "Retry provisioning" when credentials are already satisfied (this label branch existed but rendered "Save").

No data-flow changes — the page already polled and passed provisioning; this is presentation only.

Testing

• New ComputeProviderSection.client.test.tsx covering the building, failed-with-error, failed-without-error, and idle states.
• pnpm lint:fast, pnpm check-types:fast, pnpm knip all pass.

[roomote-roomote]

No code issues found. See task

Reviewed this presentation-only change: the button now reads Provisioning.../Retry provisioning (matching the setup wizard) and a failed run surfaces its persisted error inline. Data flow is unchanged — ComputeProviders already polls compute.status while a run is building and passes the per-provider provisioning state (including error) into the section. The building/failed branches are mutually exclusive and render inside the expanded section. The new ComputeProviderSection.client.test.tsx covers the building, failed-with-error, failed-without-error, and idle states and passes locally.