fix(orchestration): add circuit breaker and parallel step execution (#2168, #2172)

[mrveiss]

Summary

• Bug: Circuit breaker not integrated into orchestration WorkflowExecutor #2168: Adds @circuit_breaker_async + @retry_async decorators to _execute_coordinated_step, restoring the protection that was lost when Code Smell: Refactor 178 god class patterns #381 extracted this code from enhanced_orchestrator.py
• Bug: ParallelExecutor not integrated into orchestration WorkflowExecutor #2172: Adds dependency-aware parallel step execution via _group_steps_by_dependency() topological sort and asyncio.gather in _execute_step_group()

Changes

• _group_steps_by_dependency(): Groups steps by dependency order; independent steps form a parallel group
• _execute_step_group(): Runs single-step groups sequentially, multi-step groups via asyncio.gather
• execute_coordinated_workflow(): Now processes step groups instead of individual steps
• _execute_coordinated_step(): Protected by circuit breaker (workflow_step_execution, 3 failures → open) and retry (2 attempts, exponential backoff)
• Falls back to sequential execution on circular dependencies with error log

Test plan

• Workflow with sequential steps (A→B→C) executes in order
• Workflow with independent steps (A, B, C no deps) runs in parallel
• Mixed: A runs first, B+C run parallel (both depend on A only)
• Circuit breaker: after 3 step failures, subsequent steps fast-fail
• Circular dependency: logs error and falls back to sequential

Closes #2168
Closes #2172

[github-actions]

✅ SSOT Configuration Compliance: Passing

🎉 No hardcoded values detected that have SSOT config equivalents!