test: cover all chunked multi-get callers

[arapov]

Summary

• add >10-id chunking coverage for get_opportunities, get_projects, and get_tasks after the chunkedMultiGet refactor
• assert embed propagation for the opportunity/project multi-chunk paths
• refresh the stale get_tasks comment and HOWTO test count

Verification

• npm run format:check
• npm test -- tests/opportunities.test.ts tests/projects.test.ts tests/tasks.test.ts tests/parties.test.ts tests/mcp-integration.test.ts
• npm run typecheck
• npm run lint
• npm run build
• npm test
• git diff --check