[codex] Raise coverage threshold with focused tests

[andrewkoltsov]

Summary

• add a Vitest branch coverage threshold at 80%
• expand focused unit coverage for LibrusSession, auth photo CLI paths, render edge cases, and release-notes parsing
• keep public SDK and CLI behavior unchanged while raising dynamic-analysis evidence

Why

Branch coverage was still below the documented target even though the existing suite passed locally. This change closes the known weak branches and makes the coverage gate enforceable in CI.

Validation

• npm test
• npm run test:coverage
• npm run lint
• npx prettier --check test/cli-supporting.test.ts test/librus-session.test.ts test/release-notes.test.ts test/render.test.ts vitest.config.ts

Notes

• Repo-wide npm run format:check still reports the unrelated untracked .tasks/README.md, which is intentionally excluded from this PR.
• This PR contains only the coverage-threshold and targeted test changes.