feat(mcp): expose multimodal bundles and smoke test

[MarinaMackay]

Summary

Part 6 of the multimodal repository knowledge stack.

This slice addresses polish/hardening after review-risk audit:

• wire persisted multimodal bundles into the production MCP server via --multimodal-bundle;
• expose search_visual_context, get_visual_evidence, and find_visual_code_links through MCP;
• add a reproducible scripts/smoke_multimodal_vlm.py path for local deterministic and optional real VLM smoke tests;
• extract bounded embedded SVG text from real repository diagrams for a less-demo deterministic fallback.

Testing

python -m pytest test/scripts/test_build_multimodal_knowledge.py test/scripts/test_smoke_multimodal_vlm.py test/wiki test/web/test_config.py
python -m py_compile codenib/cli.py codenib/mcp/context.py codenib/mcp/server.py scripts/smoke_multimodal_vlm.py test/mcp/test_mcp_server.py

Latest local result:

414 passed

Note: full MCP tests require the codenib[mcp] extra. This local environment is missing mcp.types, so MCP files were checked with py_compile and the bundle router path is covered by unit tests added in test/mcp/test_mcp_server.py for MCP-enabled CI.

[MarinaMackay]

Update after comparing against nearby OSS patterns (GitDiagram / CodeGraph / OpenKB / Open Zread): this PR6 hardening slice now includes four concrete productization additions:

1. Incremental bundle update CLI

python scripts/update_multimodal_knowledge.py /path/to/repository \
  --previous /tmp/old-multimodal-knowledge.json \
  --output /tmp/new-multimodal-knowledge.json

It reuses unchanged VisualFactPacks and regenerates only added/changed media artifacts.

2. Validated visual graph plans

Adds codenib.visual-graph-plan.v1 / codenib.visual-graph-manifest.v1, validates node ids, edge endpoints, source paths, limits, and plan hashes, then compiles plans to Mermaid.

3. Agent-friendly MCP exploration tool

Adds explore_visual_context on top of the existing lower-level visual tools so agents can get visual search, optional evidence, and optional source links in one call.

4. HTML smoke preview

smoke_multimodal_vlm.py can now write a self-contained HTML preview showing SVG artifact, extracted entities, claims, source bindings, Mermaid graph plan, and tool output.

Latest local validation on the full PR6 stack:

python -m pytest test/scripts/test_build_multimodal_knowledge.py test/scripts/test_update_multimodal_knowledge.py test/scripts/test_smoke_multimodal_vlm.py test/wiki test/web/test_config.py
# 421 passed