fix(ci): isolate CLI update acceptance home

[pallyoung]

What changed

• isolate both legacy and current CLI home directories during packaged update acceptance
• keep CODER_STUDIO_HOME compatible with the legacy ~/.coder-studio layout so restart preserves host, port, and state directory
• run deterministic updater fault scenarios from the candidate package rather than the previous package
• retry fault scenario installs while the startup update check is active

Why

The 0.5.6 to 0.5.8 candidate acceptance installed and restarted successfully, but the legacy CLI wrote its config under the runner's real home while 0.5.8 read the isolated CODER_STUDIO_HOME. The restarted service therefore moved from the reserved acceptance port to 4173 and the verifier kept polling stale state. Fault scenarios also exercised the old worker instead of the candidate worker.

Impact

This changes release acceptance only. It does not alter the published CLI package or require a Changeset; npm 0.5.8 remains byte-identical and reusable.

Validation

• pnpm exec vitest run --config scripts/vitest.config.ts --environment node scripts/verify-cli-update.test.ts (11/11 passed)
• pnpm ci:typecheck:strict (passed)
• full WSL packaged acceptance against npm 0.5.6 -> 0.5.8 via rc-31682038696-1 (passed, including permission/install/restart failures)
• pnpm ci:test:scripts was also run locally; 8 unrelated Windows-platform tests fail on symlink privileges, POSIX path/executable assumptions, and the Husky shell fixture. The targeted suite above passes.