test(cli): retry flaky subprocess evaluations in CI

[vianmora]

Description

The CLI evaluation tests under packages/cli/evaluations/high-impact/* spawn real CLI subprocesses (cold-started through tsx) against a local fixture API. On a loaded CI runner those cold starts occasionally exceed the default 15s test timeout, so fixture-api.test.ts fails with Test timed out in 15000ms even though nothing is broken. Re-running the same commit passes. It is a timing/flaky failure, not a regression.

This adds a CI-only test retry so a transient timeout is absorbed instead of turning the whole run red and requiring a manual re-run:

// packages/cli/vite.config.ts
test: {
  retry: process.env.CI ? 2 : 0,
}

• A real failure still fails every attempt, so this hides no bug.
• Local runs stay strict (retry: 0).
• The defineConfig import moves from vite to vitest/config (a superset; the existing build block is unaffected) so the test field type-checks.
• It lives in packages/cli/vite.config.ts because that is the config Vitest loads for this package. A test.retry in the root vitest.config.ts does not reach it (verified locally with a probe test: the root value is ignored, the package-local one takes effect).

Steps for reproduction

1. Run the CLI package tests repeatedly, ideally on a busy machine: pnpm --filter=webstudio test.
2. Occasionally evaluations/high-impact/fixture-api.test.ts fails with Test timed out in 15000ms; a re-run passes.
3. With this change and CI=1, the transient timeout is retried up to 2x instead of failing the run.

Code Review

• hi @kof, I need you to do
  • conceptual review (architecture, feature-correctness)

Before requesting a review

• made a self-review
• added inline comments where things may be not obvious (the "why", not "what")

Before merging

• tested locally (verified the retry applies from the package config; the root config value is ignored)
• tested on preview environment (n/a, test-runner config change with no preview surface)
• updated test cases document (n/a, no feature change)
• added tests (n/a, adjusts existing test-runner behavior)
• if any new env variables are added, added them to .env file (none added; process.env.CI is set by CI providers)