Flag newly disabled deploy tests (#96505)
## What changed
Added scoped review guidance under `test/` so Vercel Agent flags changes
that newly disable deploy-mode tests or assertions.
## Why
Deploy coverage should only be disabled for assertions that are
inherently self-hosted-specific. When deployed behavior differs, the
test should prefer documenting those semantics instead of skipping
deploy mode.
## Validation
- `pnpm install --frozen-lockfile`
- `pnpm build-all`
- Hosted Vercel Agent E2E: an intentional `skipDeployment: true` probe
was flagged inline, then removed
- Hosted Vercel Agent Review passed on the final diff
