Fix the remaining frontend lint warnings (only-export-components, immutability)

[regnull]

Goal

Fix the remaining pnpm lint warnings, react(only-export-components) and react(immutability), so the frontend lints with no warnings at all.

Context

src/components/RunCard.tsx:15:17     react(only-export-components)
src/pages/BotPage.tsx:18:17          react(only-export-components)
src/pages/ThreadPage.test.tsx:69:5   react(immutability)
src/pages/ThreadPage.test.tsx:70:5   react(immutability)

only-export-components means a file exports something other than components (a helper or constant), which breaks React Fast Refresh for that file. Moving the non-component export into its own module is usually enough. The immutability warnings are in a test that assigns to a value React treats as immutable.

This complements the set-state-in-effect issue; either can be done first.

Acceptance criteria

• These four warnings are gone
• pnpm test and pnpm typecheck pass