feat(ui): add knowledge graph view

[netclectic]

Summary

Add a knowledge graph view to visualize memories and their relationships.

Changes

• New IGraphService (auto-registered via [AutoRegisterInterfaces]; does not extend IStorage) returning all non-archived memories as nodes and their relationships as edges, optionally scoped to a workspace subtree or a single project.
• New endpoints in HomeController: GET /api/graph?workspaceId=&projectId= and the /graph page.
• New Views/Home/Graph.cshtml rendering with vis-network 10.1.0, self-hosted at wwwroot/js/vis-network.min.js (no external CDN dependency).
• Node size ∝ incoming relationship count (indegree); nodes are unlabeled dots with titles shown only on hover (theme-aware tooltips); node color by memory type, edge color by relationship type; click navigates to the memory.
• Zoom in / out / fit controls (works without a mouse wheel).
• Sidebar navigation link and progressive loading UX with a hard timeout.

Testing

• 195 unit tests pass, 188 integration tests pass (includes graph service integration tests for nodes/edges/scope).

Related

• Add a knowledge graph view netclectic/memorizer#4