test: expand risk-based coverage

[crypt0rr]

Summary

• Add high-risk Go regressions for late successful scan results after cancellation, transactional host-projection repair, SSE cursor reservation recovery, and listener shutdown.
• Expand frontend behavior coverage for dashboard recovery, host evidence fallback, job detail lifecycle, job editor safety, and scanner-profile workflows.
• Keep production behavior unchanged; this PR adds tests only.

Validation

• Frontend coverage: 371 tests; 94.14% statements, 96.13% lines, 86.68% branches, 91.84% functions.
• Full Go race suite and package coverage gate passed (87.9% aggregate).
• Frontend lint/build and Playwright: 115 passed, 149 viewport-specific skips.
• Go vet and diff checks passed.