fix: resolve typescript lint errors and test failures

- Remove unnecessary `any` casts and unsafe type assertions in `useAgentStream.ts`.
- Introduce `MinimalTrackedToolCall` to safely type mock tool calls for inactivity monitors.
- Fix arrow-body-style lint errors in `AppContainer.tsx` and `useAgentStream.ts`.
- Update `nonInteractiveCli.test.ts` to include a required `build` method in mock tools to prevent TypeErrors during stream initialization.
- Remove redundant non-null assertion in `legacy-agent-session.ts`.