AI assistant migrated to centralized workflowDocumentStore

The AI assistant's connection queries are being routed through a centralized facade instead of directly accessing multiple store APIs. Three files in the editor's AI assistant feature — focused nodes tracking, builder todos, and the builder store itself — are being updated to pull connection data from workflowDocumentStore rather than workflowsStore or workflowState.

This is part of a larger architectural effort to consolidate how workflow connections are accessed. The workflowDocumentStore serves as a single interface for connection data, replacing scattered direct store access throughout the codebase. Using a facade means changes to how connections are stored only need to happen in one place.

The changes are minimal in scope — replacing one set of accessor calls with equivalents from the new facade — but they position the AI assistant for easier maintenance as the underlying data layer evolves.