POC: Validate DevExpress DiagramControl for diagram replacement

[msevestre]

Context

Phase 0 of #2320 (Replace GoDiagram with DevExpress DiagramControl). This is a go/no-go gate — if the POC fails, we evaluate alternatives before proceeding.

Goal

Add a throwaway MoBi.DiagramPoc WinForms project to the MoBi solution. Prove three things with standalone, hardcoded examples (no integration with real domain model):

1. Custom shapes with port-specific drag-to-connect

• Create a reaction node (triangle/Y-shape) with 3 colored connection points: blue (educt), green (product), red (modifier)
• Create a molecule node (circle) with 1 connection point
• Drag from molecule → reaction port creates a connector colored to match the target port
• Validate that connections are port-specific (e.g., can distinguish which port was connected to)

2. Nested containers with expand/collapse

• Create containers 3+ levels deep (e.g., Organism → Organ → Compartment → SubCompartment)
• Expand/collapse works at each level
• Child nodes stay inside parent containers visually

3. Sugiyama auto-layout

• Build a small reaction network: ~5 molecule nodes, ~3 reaction nodes, wired together
• Apply ApplySugiyamaLayout() and verify the result is readable

Done when

• All 3 capabilities demonstrated in the POC project
• Or: documented which capability fails and why, so the team can evaluate alternatives

Notes

• Throwaway code — no tests, no architecture, no domain model integration
• Delete MoBi.DiagramPoc project after validation
• Build against DevExpress 21.2 (current version)