Canvas operations refactored to use document store facade

n8n's editor canvas is getting a structural update. Canvas operations that previously accessed the workflow object directly have been refactored to use a centralized document store facade instead.

The change consolidates how node and connection data is queried across the canvas. Instead of reaching into workflowObject for operations like retrieving parent nodes, finding connected nodes, or fetching workflow metadata, all calls now flow through workflowDocumentStore. This creates a cleaner boundary between the workflow data layer and UI operations.

The refactoring removes a standalone helper function and relocates its logic into the document store module where it belongs. Optional chaining is applied throughout, making the code more defensive against null values.

This is foundational work. By establishing a consistent access pattern now, the codebase will be better positioned to adopt CRDT for collaborative editing. Users won't see any change in behavior today, but the architecture is becoming more amenable to conflict resolution in distributed scenarios.