Rename rendered → canvas across the graph path and add Canvas terminology

[kmcginnes]

Task

Rename rendered → canvas across the graph render path, and establish "Canvas" as the ubiquitous term for on-graph entities in CONTEXT.md. Pure rename plus terminology — no behavior change.

Details

• Branded types: RenderedVertexId → CanvasVertexId, RenderedEdgeId → CanvasEdgeId.
• Rename the converter module (renderedEntities → canvasEntities) and its test.
• Rename the id helpers, converter functions, hooks, and element types (RenderedVertex/RenderedEdge → Canvas*) and all call sites (~11 files, including the Graph View, context menu, node badges, badge renderer, global actions, Schema View sidebar, state-provider index).
• Collision check (done): target names (CanvasVertexId, CanvasEdgeId, toCanvasVertex/Edge, useCanvasVertices/Edges, canvasEntities) do not currently exist. Existing canvas usage is the unrelated HTML/cytoscape-canvas sense (CytoscapeCanvas, cyCanvas, getCanvas) — no conflict.
• CONTEXT.md: add a Canvas Vertex / Canvas Edge term (the structural, id-prefixed representation Cytoscape renders) and record the rendered → canvas rename under Flagged ambiguities, consistent with the other legacy-term migrations.

Acceptance

• No rendered/Rendered* identifiers remain in the graph path (verified by grep).
• pnpm check:types and pnpm test green.
• CONTEXT.md carries the Canvas terminology.

Related Issues

• Parent Reconcile the graph canvas — stop rebuilding on every change #1887

Important

Internal only — this issue is maintained by the core team and is not accepting external contributions.