[Do not review] fix: normalize Argo conditional execution

[talsperre]

Summary

• normalize conditional nodes behind stable public wrappers and use success barriers for graph dependencies
• cover conditional foreach, recursive switches, and conditional parallel/JobSet templates
• use direct recursive switch output selection for legacy DAG exits, avoiding the nested-foreach expression regression while retaining safe navigation for non-recursive switches
• add regression coverage for simple, nested, sequential, recursive, foreach, parallel, failure, and skip-chain shapes

This PR is stacked on #3344 and targets its head branch so it contains only the follow-up normalization.

Verification

• 35 Argo-focused unit tests passed
• all pre-commit hooks passed
• Python compilation and git diff --check passed
• Argo 3.7.11 E2E passed for active/inactive conditional foreach, selected branch failure propagation, recursive conditionals, and recursive conditionals inside foreach
• Argo 3.6.0 controller and executor E2E passed for inactive conditional foreach, selected branch failure propagation, and recursive conditionals inside foreach
• three independent code reviews found no remaining correctness or minimality blocker

Remaining live-test caveat

Conditional @parallel/JobSet generation is covered structurally, but was not run against a live JobSet controller because the local stack did not install one.