Add cycle/loop detection in message flow

[lowhung]

Summary

Detect and highlight cycles in the message flow graph. Cycles can indicate feedback loops, potential deadlocks, or architectural issues.

Why Detect Cycles?

• Feedback loops: Module A → B → C → A can cause cascading updates
• Deadlock risk: Circular dependencies in request/response patterns
• Design review: Sometimes cycles are intentional, sometimes bugs
• Debugging: Helps understand why messages are multiplying

Proposed Features

Cycle Detection

• Find all strongly connected components (SCCs) with >1 node
• Identify specific edges that form cycles
• Distinguish between:
  • Simple cycles (A → B → A)
  • Complex cycles (A → B → C → A)
  • Nested cycles

Visualization

• Highlight cycle edges with distinct color (e.g., orange)
• Add cycle indicator icon on participating nodes
• Optional: animate flow direction in cycle
• "Cycle view" mode that dims non-cycle elements

Cycle Panel

• List detected cycles
• Show nodes involved in each cycle
• Cycle length and involved topics
• Click to focus on cycle

Acceptance Criteria

• Detect all cycles in graph
• Visual highlighting of cycle edges
• Cycle list in side panel
• Click-to-focus on cycles
• Handle overlapping cycles

Technical Notes

• Use Tarjan's or Kosaraju's algorithm for SCC detection
• petgraph has tarjan_scc() built-in
• Consider performance for large graphs