fix(graph): enhance start node and end node layout

[yassinedorbozgithub]

Screenshots

• After the fix

• Before the fix

Summary

This PR improves the graph layout by enhancing the positioning of the workflow Start and End nodes. The updated layout ensures these nodes are consistently aligned with the main execution flow, producing cleaner and more predictable workflow diagrams.

Why

The previous positioning of the Start and End nodes could lead to inconsistent layouts, making workflows harder to read—especially in larger or more complex graphs. Aligning these entry and exit points improves visual clarity and creates a more polished editing experience.

How to review

Focus on the graph layout changes, specifically:

• Verify the Start node is consistently positioned at the beginning of the workflow.
• Verify the End node is consistently positioned at the end of the workflow.
• Check workflows with linear, conditional, parallel, and nested branches to ensure the new positioning behaves correctly without introducing regressions.
• Confirm edge routing remains clean and node spacing is preserved.

Validation

• Tested workflows containing simple linear flows.
• Tested workflows with conditional and parallel branches.
• Verified Start and End node alignment after layout re-computation.
• Confirmed there are no regressions in node positioning, edge routing, or overall graph spacing.