Reverts the Preparing component changes from b2857110b so the progress bar
turns red (bg-destructive) and the error text shows below it when boot.error
is set, instead of bailing out with an early return null.
The corresponding e2e guard in waitForBootFailure (e2e/fixtures.ts) that
rejected any progress bar in the DOM is dropped — it now waits for the
failure dialog (Retry/Repair/Use local gateway/Connection settings) or the
"Desktop boot failed" toast. The boot-failure.spec.ts header comment is
updated to match.
Verified: tsc clean, vitest boot-failure-reauth (21/21) + boot-failure-overlay
(3/3) pass, npm run build clean, playwright e2e/boot-failure.spec.ts 2/2 pass.
33c154e41f