feat(command-center): instance-centric routing view with collapsible agent sections

- Extract formatInstanceLabel and isGroupInstance to shared formatting.ts (DRY)
- Add InstanceRoutingView component replacing file-centric FileRoutingCards
  - Collapsible sections per base agent type with file/instance counts
  - Instance group cards showing grouped vs ungrouped files
  - File chips with tooltip reasoning, priority, and confidence
  - Correlates routing decisions (base types) with agent instance states (compound IDs)
  - Graceful degradation when instances haven't started yet
- Thread allAgentStates through AgentSectionsProps to OrchestratorSections
- Wire InstanceRoutingView in NodeDetailsSidebar File Routing Table section
- Update barrel export (replace FileRoutingCards with InstanceRoutingView)

Author: Siddharth-Khattar