feat: LegionControl - Multi-Agent DAG topology orchestration

[1688mengdie]

Summary

Add LegionControl tool for dynamic DAG topology-based multi-agent orchestration.

Changes

• LegionControl tool: Read JSON template -> topological sort -> layered session creation -> context injection -> serial/parallel dispatch
• Preset storage: CRUD operations for legion templates stored as JSON files
• Conditional edge support: Edges with empty condition field are skipped in cycle detection
• Rollback on failure: Automatically cleans up created sessions if any node creation fails
• Commander prompt rewrite: Replaces gstack skills workflow with legion commander + Gate Loop Protocol
• SessionControlAgentType: Changed from hardcoded enum to dynamic struct for flexible agent type routing
• Post-call hooks extension: Added HookResult enum and Stop hook infrastructure for round-level behavior guards

Verification

• cargo check -p bitfun-desktop
• LegionControl list/load tested in Team mode (feature branch)
• Conditional edges skip cycle detection
• Rollback deletes partial sessions on failure