fix: resolve CI lint and test failures for PR #1009

- Prune stale eslint-suppressions.json entries (--prune-suppressions)
- Update test assertions to match guided error output ('Unknown Tool'
  instead of 'Tool Call Format Error') in presentAssistantMessage-custom-tool.spec.ts
  and presentAssistantMessage-unknown-tool.spec.ts
- Remove AI session notes docs/260726_0003_session_error-hiding-fix/

Author: Zoo (VP)