ui(results): ResultsTab isLoading must not hide errorMessage

[ZhuchkaTriplesix]

Parent

Part of #445

Severity

Low

Problem

isLoading always wins over errorMessage. Fine if callers clear error on run (SQL workspaces do); any caller that sets both shows spinner and hides the error.

Evidence

• lib/features/main_screen/results_tab.dart (~45–50)

Acceptance

• Document invariant or show error when !isLoading
• Test asserting error visible when loading is false with error set
• Optional: assert/test that workspaces clear error before setting loading

Suggested fix

Prefer error when errorMessage != null && !isLoading; document caller contract in dartdoc.

[ZhuchkaTriplesix]

Shipped on dev via #462 (Closes did not auto-close because PRs targeted dev).