fix: resolve leftover conflict markers in MCP docs

[Frankie-Xu]

Summary

• Union leftover #146 / #147 conflict markers in docs/en/mcp.md and docs/zh/mcp.md so the published MCP tool table lists both export_jsonld and export_cypher after export_csv.
• Follow-up sentences now name all four graph exports; the example session includes both new calls.
• Add tests/docs/test_no_conflict_markers.py so leftover <<<<<<< / ======= / >>>>>>> lines fail CI.

Closes yifanfeng97#148

Out of scope

• MCP server code
• README (already lists both tools)
• MCP write tools or scope parameters

Test plan

• uv run pytest tests/docs/test_no_conflict_markers.py -q
• Visual check that neither MCP page still contains conflict markers

  

[Frankie-Xu]

Opened on the fork by mistake. Review is at yifanfeng97#149 — closing this.