[codex] Align local and CI test checks

[piers-sinclair]

Summary

• add frontend unit tests to frontend CI
• expand local ci-check to run frontend lint, format, generated API verification, Vitest, build, and Playwright
• keep backend unit coverage gated at 80%, but run integration tests without a line-coverage gate
• update docs to describe the new test/coverage policy

Validation

• dotnet build -c Release

Notes

• bash-based script checks could not be executed locally because this Windows host maps bash to WSL and no WSL distribution is installed.
• Initial dotnet build attempts were blocked by sandbox access to the user NuGet.Config; rerunning with approved filesystem access passed.