Isolate standalone Playwright visual fixtures from production E2E discovery

Standalone visual-fixture specs under a broad Playwright test directory should be explicitly isolated from the production suite. When a fixture depends on its own Vite server or custom configuration, add its path to the main Playwright config's testIgnore and give it a dedicated script/config; otherwise CI can auto-discover the spec against the production app and fail on a fixture-only route. This applies when test roots overlap; repositories with separate non-overlapping test roots do not need this safeguard.

Evidence/example — 2026-09-11: In the theft repository for PR #844, the dedicated responsive fixture passed locally, but the production browser suite auto-discovered it and failed because its fixture-only route was unavailable. Adding testIgnore to the primary Playwright config, following the repository's existing isolation pattern, made the corrected production browser suite pass. Sources: GitHub Actions CI runs 34554871454 and 34555293815; repository Playwright configurations.