feat(knowledge): add interactive knowledge graph visualization

[Winsaney]

Summary

• add an interactive Google OKF-style visualization to the existing Knowledge Graph section
• preserve the existing card view and full concept viewer
• add graph search, type filtering, layouts, archived-node handling, relationship details, and large-graph safeguards
• render Markdown summaries in the desktop node detail panel, including legacy flattened tables and lists
• support both inline and fullscreen desktop graph views

Validation

• npm --prefix frontend-enterprise test — 18 files, 63 tests passed
• npm --prefix frontend-enterprise run build
• npm --prefix frontend-enterprise run config:check
• desktop inline and fullscreen browser QA
• no browser console warnings or errors

Notes

• i18n:check continues to report 184 pre-existing missing translations on the current upstream main; this PR adds no new missing translations.
• No backend API or database schema changes are required.
• Adds Cytoscape as a frontend dependency.
• Mobile layout is intentionally out of scope.

Closes #74

[Winsaney]

Desktop screenshots

Inline and fullscreen views: