fix: restore visual summary reports

Summary

• Fixes: POST /api/visual/summary-report returns HTTP 500 instead of a rendered report for valid scan-summary JSON, including the nmap workflow reported in issue #146.
• Root cause: The route instantiates ModernVisualEngine and calls create_summary_report, but that renderer was accidentally defined on the unrelated CVEIntelligenceManager class, so every valid request raises AttributeError.

Fixes #146.

Regression evidence

• Before: python tests/test_visual_summary_report.py -v exited 1

• After: python tests/test_visual_summary_report.py -v exited 0

Verification

• python -m unittest discover -s tests -v
• python -m py_compile hexstrike_server.py hexstrike_mcp.py tests/test_visual_summary_report.py

Scope

• 2 files changed, +90 / -27 lines